//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21505 SUBJECT: LIGO/Virgo G298048: Fermi GBM trigger 524666471/170817529: LIGO/Virgo Identification of a possible gravitational-wave counterpart DATE: 17/08/17 13:21:42 GMT FROM: Reed Clasey Essick at MIT The LIGO Scientific Collaboration and the Virgo Collaboration report: The online CBC pipeline (gstlal) has made a preliminary identification of a GW candidate associated with the time of Fermi GBM trigger 524666471/170817529 at gps time 1187008884.47 (Thu Aug 17 12:41:06 GMT 2017) with RA=186.62deg Dec=-48.84deg and an error radius of 17.45deg. The candidate is consistent with a neutron star binary coalescence with False Alarm Rate of ~1/10,000 years. An offline analysis is ongoing. Any significant updates will be provided by a new Circular. [GCN OPS NOTE(17aug17): Per author's request, the LIGO/VIRGO ID was added to the beginning of the Subject-line.] //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21506 SUBJECT: LIGO/Virgo G298048: Fermi GBM trigger 170817.529 and LIGO single IFO trigger DATE: 17/08/17 13:47:37 GMT FROM: Valerie Connaughton at USRA V. Connaughton (USRA) reports on behalf of the GBM-LIGO Group: L. Blackburn (CfA), M. S. Briggs (UAH), J. Broida (Carleton College), E. Burns (NASA/GSFC), J. Camp (NASA/GSFC), T. Dal Canton (NASA/GSFC), N. Christensen (Carleton College), A. Goldstein (USRA), R. Hamburg (UAH), C. M. Hui (NASA/MSFC), P. Jenke (UAH), D. Kocevski (NASA/MSFC), N. Leroy (LAL), T. Littenberg (NASA/MSFC), J. McEnery (NASA/GSFC), R. Preece (UAH), J. Racusin (NASA/GSFC), P. Shawhan (UMD), K. Siellez (GA Tech), L. Singer (NASA/GSFC), J. Veitch (Birmingham), P. Veres (UAH), and C. Wilson-Hodge (NASA/MSFC) The on-board trigger time of Fermi GBM trigger 170817.529 524666471 at 12:41:06.47 UT is approximately 2 seconds after the single interferometer LIGO trigger reported in GCN 21505. Inspection of the real-time data suggests the trigger is consistent with a weak short GRB, location RA, Dec = 176.8, -39.8 deg (J2000). The statistical uncertainty on this location is 11.6 deg (radius, 1-sigma containment, statistical only; there is additionally a systematic error which we have characterized as a core-plus-tail model, with 90% of GRBs having a 3.7 deg error and a small tail suffering a larger than 10 deg systematic error. [Connaughton et al. 2015, ApJS, 216, 32] ) The GBM localization sky map for this event is available at the Fermi Science Support Center and shows the uncertainty region including the systematic component: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2017/bn170817529/quicklook/glg_locplot_all_bn170817529.png and as a FITS file: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2017/bn170817529/quicklook/glg_locprob_all_bn170817529.fit We are producing a HEALPIX map for dissemination to the lv-em observers which should be available very shortly and will report further analysis of this event when the science data are downlinked from the spacecraft, on a time-scale of hours. [GCN OPS NOTE(17aug17): Per author's request, the LIGO/VIRGO ID was added to the beginning of the Subject-line.] //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21507 SUBJECT: LIGO/Virgo G298048: INTEGRAL detection of a prompt gamma-ray counterpart DATE: 17/08/17 13:57:47 GMT FROM: Volodymyr Savchenko at APC,Paris V. Savchenko (ISDC, University of Geneva, CH) on behalf of the INTEGRAL group: S. Mereghetti (IASF-Milano, Italy), C. Ferrigno ((ISDC, University of Geneva, CH), E. Kuulkers (ESTEC/ESA, The Netherlands), A. Bazzano (IAPS-Roma, Italy), E. Bozzo, T. J.-L. Courvoisier (ISDC, University of Geneva, CH) S. Brandt (DTU - Denmark) R. Diehl (MPE-Garching, Germany) L. Hanlon (UCD, Ireland) P. Laurent (APC, Saclay/CEA, France) A. Lutovinov (IKI, Russia) J.P. Roques (CESR, France) R. Sunyaev (IKI, Russia) P. Ubertini (IAPS-Roma, Italy) We investigated serendipitous INTEGRAL observations carried out at the time of the LIGO/Virgo burst candidate G298048. The satellite was covering a fraction of the probability of the LIGO-Virgo localization. The best sensitivity depends on the source location. We investigated the SPI-ACS light curves between -30 and +30 s from the trigger time (2017-08-17 12:41:04 UTC, T0) on temporal scales from 0.1 to 100s. In the SPI-ACS data, we detect a short and relatively weak transient with S/N of at T0, with an S/N larger than 3. coincident with the GBM trigger (Connaughton 2017, GCN 21506). Further analysis is ongoing, and will be reported in the coming circulars. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21508 SUBJECT: LIGO/Virgo G298048: FOUND COINCIDENT IceCube neutrino observation DATE: 17/08/17 14:05:11 GMT FROM: Stefan Countryman at LIGO Scientific Collaboration I. Bartos, S. Countryman (Columbia), C. Finley (U Stockholm), E. Blaufuss (U Maryland), R. Corley, Z. Marka, S. Marka (Columbia) on behalf of the IceCube Collaboration The analysis FOUND A COINCIDENT ONLINE TRACK-LIKE NEUTRINO CANDIDATE detected by IceCube within the 500 second window surrounding G298048 within the BAYESTAR skymap. The coordinates of the reconstructed neutrino source are below: # dt[s] RA[deg] Dec[deg] E[TeV] Sigma[deg] ------------------------------------------------------------------ 1. -166.00 291.4 69.0 0.37 3.1 We searched IceCube online track-like neutrino candidates (GFU) detected in a [-500,500] second interval about the LIGO-Virgo trigger G298048. We compared the candidate source directions of 6 temporally-coincident neutrinos to the BAYESTAR skymap, with the following parameters: # dt[s] RA[deg] Dec[deg] E[TeV] Sigma[deg] ------------------------------------------------------------------ 1. -419.79 226.7 12.0 0.65 1.8 2. -266.61 239.6 19.6 1.04 1.6 3. -165.72 291.3 68.8 0.37 3.1 4. -153.47 182.0 -3.2 0.88 0.9 5. 310.59 1.4 23.8 0.50 1.5 6. 390.94 203.2 6.0 1.00 0.7 (dt--time from GW in [seconds]; RA/Dec--sky location in [degrees]; E--reconstructed secondary muon energy in [TeV]; Sigma--uncertainty of direction reconstruction in [degrees]) A coincident neutrino-GW skymap has been posted to GraceDB (). A JSON-formatted list of the above neutrinos can be downloaded from GraceDB at: In addition, we are performing coincident searches with other IceCube data streams, including the high-energy starting events (HESE) and Supernova triggers. HESE events have typical energies > 60 TeV and start inside the detector volume, leading to a relatively pure event sample with a high fraction of astrophysical neutrinos. The SN trigger system is sensitive to sudden increases in photomultiplier counts across the detector, which could indicate a burst of MeV neutrinos. We will submit separate GCN circulars if coincident HESE or SN triggers are found. The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. For a description of the IceCube realtime alert system, please refer to ; for more information on joint neutrino and gravitational wave searches, please refer to . //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21509 SUBJECT: LIGO/Virgo G298048: Identification of a binary neutron star candidate coincident with Fermi GBM trigger 524666471/170817529 DATE: 17/08/17 14:09:25 GMT FROM: Reed Clasey Essick at MIT The LIGO Scientific Collaboration and the Virgo Collaboration report: A binary neutron star candidate was identified in data from the LIGO Hanford detector at gps time 1187008882.4457 (Thu Aug 17 12:41:04 GMT 2017). The signal is clearly visible in time-frequency representations of the gravitational-wave strain in data from H1. The current significance estimate of ~1/10,000 years is based on data from H1 alone. Information about this candidate is available in GraceDb here https://gracedb.ligo.org/events/view/G298048 The effective distance to this candidate is approximately 58 Mpc and the current localization estimate using gravitational-wave data alone is quite broad because it only makes use of data from H1. We note that this is only an estimate of the effective distance, and the actual luminosity distance to the source is likely larger. The neutron star coalescence candidate is also clearly visible in data from the LIGO Livingston detector, although there is a coincident noise artifact in the L1 data. To be clear, the binary neutron star candidate is clearly visible in the L1 data on top of the noise artifact. There is no evidence for any noise artifact at H1. Virgo was online at the time, although its data was not used to estimate the candidate’s significance. It is expected to be visible in all detectors once the data has been analyzed. The gravitational-wave candidate was found in coincidence with Fermi GBM trigger 524666471/170817529, which occurred at gps time 1187008884.47 (Thu Aug 17 12:41:06 GMT 2017). This is approximately 2 seconds after the gravitational-wave candidate’s coalescence time. The Fermi trigger’s localization estimate from Fermi data alone can be found here https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2017/bn170817529/quicklook/glg_locplot_all_bn170817529.png https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2017/bn170817529/quicklook/glg_locprob_all_bn170817529.fit Analyses including data from H1, L1, and V1 are ongoing and a sky-map using gravitational-wave data will be made available as quickly as possible. [GCN OPS NOTE(17aug17): Per author's request, the LIGO/VIRGO ID was added to the beginning of the Subject-line.] //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21510 SUBJECT: LIGO/Virgo G298048: correction to the luminosity distance reported in GCN 21509 DATE: 17/08/17 14:38:46 GMT FROM: Leo Singer at NASA/GSFC The LIGO Scientific Collaboration and the Virgo Collaboration report: In GCN 21509, we reported the identification of a binary neutron star candidate. We had stated that actual luminosity distance to the source is likely larger than the estimated effective distance. The effective distance quoted estimates the *maximum* distance to the source and so the actual luminosity distance is can be *smaller* than the estimate of the effective distance. The BAYESTAR localization generated from H1 data only estimates an actual luminosity distance of 37 +/- 12 Mpc (a posteriori mean +/- standard deviation). The distance estimate will likely evolve with further offline follow-up using data from H1, L1, and V1. Analyses including data from H1, L1, and V1 are still ongoing and a sky-map using gravitational-wave data will be made available as quickly as possible. [GCN OPS NOTE(17aug17): Per author's request, the LIGO/VIRGO ID was added to the beginning of the Subject-line.] //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21511 SUBJECT: LIGO/Virgo G298048: COINCIDENT IceCube neutrino candidate with Fermi GBM trigger 524666471/170817529 DATE: 17/08/17 14:54:58 GMT FROM: Imre Bartos at Columbia/LIGO I. Bartos, S. Countryman (Columbia), C. Finley (U Stockholm), E. Blaufuss (U Maryland), R. Corley, Z. Marka, S. Marka (Columbia) on behalf of the IceCube Collaboration In GCN 21508 we recently reported that the identification of IceCube neutrino candidates that are temporally and directionally coincident with LIGO/Virgo G298048. A comparison of these neutrino candidates with Fermi GBM trigger 524666471/170817529 shows that one IceCube neutrino candidate is also *directionally* coincident with 90% CL of the Fermi GRB event. The coordinates of this reconstructed neutrino source are below: # dt[s] RA[deg] Dec[deg] E[TeV] Sigma[deg] ------------------------------------------------------------------ 4. -153.47 182.0 -3.2 0.88 0.9 (dt--time from GW in [seconds]; RA/Dec--sky location in [degrees]; E--reconstructed secondary muon energy in [TeV]; Sigma--uncertainty of direction reconstruction in [degrees]) A coincident neutrino-GW skymap has been posted to GraceDB (). A JSON-formatted list of the above neutrinos can be downloaded from GraceDB at: //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21513 SUBJECT: LIGO/Virgo G298048: Further analysis of a binary neutron star candidate with updated sky localization DATE: 17/08/17 17:54:51 GMT FROM: Leo Singer at NASA/GSFC The LIGO Scientific Collaboration and the Virgo Collaboration report: We performed a preliminary offline analysis using the PyCBC search (Nitz et al. arxiv:1705.01513, 2017) of the binary neutron star candidate G298048 (LSC and Virgo, GCN 21505, 21509, 21510) identified in low-latency by the gstlal online search (Messick et al. Phys. Rev. D 95, 042001, 2017). A trigger consistent with a binary neutron star merger is observed at GPS time 1187008882.443 (2017-08-17 12:41:04 UTC) in both the LIGO Livingston (L1) and LIGO Hanford (H1) detectors. The trigger is below threshold in Virgo because of the antenna pattern for Virgo (V1) at the time and location of this event, but the Virgo instrument contributes to the localization. The duration of the gravitational-wave signal is approximately 74 seconds from the search’s low-frequency cutoff of 27 Hz to the binary merger. Investigation of L1 data identified a noise transient from a known class of instrumental glitches during the inspiral signal. The duration of this glitch is a small fraction of a second and does not appear to affect the signal at times away from the glitch. To make an improved preliminary estimate of the sky position, we re-analyzed the data, removing the L1 noise transient at GPS time 1187008881.389 by multiplying the strain data with a Tukey window, such that the total duration of the zeroed data is 0.2 s and the total duration of the Tukey window is 1.2 s. An updated BAYESTAR sky map (Singer et al. 2016, ApJL 829, 15) that uses data from all three gravitational-wave observatories (H1, L1, and V1) is available for retrieval from the GraceDB page (https://gracedb.ligo.org/events/view/G298048): bayestar-HLV.fits.gz. The centroid (maximum a posteriori) sky location is R.A.=12h57m, Dec.=-17d51m. The 50% credible region spans about 9 deg2 and the 90% region about 31 deg2. The luminosity distance is 40 +/- 8 Mpc (all-sky a posteriori mean +/- standard deviation). This is the preferred sky map at this time. If we assume that the binary is either face on or face off in the plane of the sky, then we obtain a revised estimate of luminosity distance of 50 +/- 3 Mpc. This assumption does not significantly affect the overall 2D localization projected onto the sky, but reduces the 3D volume of the localization (e.g. Pankow et al. 2017, ApJ 834, 154). We caution that the parameters and significance of this candidate may be subject to change as data-quality, calibration, and full parameter estimation studies are ongoing. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21514 SUBJECT: LIGO/Virgo G298048: Astrosat CZTI upper limits DATE: 17/08/17 18:16:42 GMT FROM: Varun Bhalerao at Indian Inst of Tech Arvind Balasubramanian (IISER Pune), Sujay Mate (IIT Bombay), Varun Bhalerao (IIT Bombay), Dipankar Bhattacharya (IUCAA), Ajay Vibhute (IUCAA), Sukanta Bose (IUCAA), Gulab Chand Dewangan (IUCAA), Ranjeev Misra (IUCAA), Sanjit Mitra (IUCAA), A R Rao (TIFR), Tarun Souradeep (IUCAA), Santosh Vadawale (PRL), on behalf of the Astrosat CZTI team report: We carried out offline analysis of data from Astrosat CZTI in a 100 second window centred on the G298048 trigger time, UT 2017-08-17 12:41:04, to look for any coincident hard X-ray flash. CZTI is a coded aperture mask instrument that has considerable effective area for about 29% of the entire sky. Based on the pointing direction of Astrosat at the time of the GW event and the Bayestar skymap provided by LVC (bayestar.fits.gz,0), the sky visible to CZTI has 12% probability of containing the EM counterpart. CZTI data were de-trended to remove orbit-wise background variation. We then searched data from the four independent, identical quadrants to look for coincident spikes in the count rates. Searches were undertaken by binning the data in 0.1s, 1s and 10s respectively. Statistical fluctuations in count rates were estimated by using data from 5 previous orbits. We selected confidence levels such that the probability of a false trigger in this 100s window is 10^-4. We do not find any evidence for any hard X-ray transient in this window. We convert our count rates into fluence and flux limits by assuming that the source spectrum has band parameters alpha = -1.0, beta = -2.5, Epeak = 300. The upper limits for source fluence and flux in a 30-200 keV band at different timescales are: Calculating fluxes assuming band parameters alpha = -1.0, beta = -2.5, Epeak = 300 0.1 s: Effective fluence limit= 6.93e-7 ergs/cm^2; flux= 6.93e-6 ergs/cm^2/s 1.0 s: Effective fluence limit= 1.65e-6 ergs/cm^2; flux= 1.65e-6 ergs/cm^2/s 10.0s: Effective fluence limit= 2.05e-6 ergs/cm^2; flux= 2.05e-7 ergs/cm^2/s The corresponding all-sky maps are uploaded at https://gracedb.ligo.org/apiweb/events/G298048/files/G298048_CZTI_limits.pdf,0 CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, ISAC, IUCAA, SAC and PRL. The Indian Space Research Organisation funded, managed and facilitated the project. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21515 SUBJECT: LIGO/Virgo G298048: IPN triangulation of Fermi/GBM trigger 524666471/170817529 DATE: 17/08/17 18:35:12 GMT FROM: Dmitry Svinkin at Ioffe Institute D. Svinkin, K. Hurley, on behalf of the IPN, A. von Kienlin, X. Zhang, A. Rau, V. Savchenko, E. Bozzo, and C. Ferrigno, on behalf of the INTEGRAL SPI-ACS GRB team, V. Connaughton, M. S. Briggs, C. Meegan, V. Pelassa, and A. Goldstein, on behalf of the Fermi GBM team, report: A short-duration burst (Connaughton, LVC GCN Circ. 21506) has been detected by Fermi (GBM; trigger 524666471), and INTEGRAL (SPI-ACS), so far, at about 45666 s UT (12:41:06). We have triangulated it to a GBM-INTEGRAL annulus centered at RA(2000)=119.131 deg (07h 56m 31s) Dec(2000)=-44.133 deg (-44d 07' 57"), whose radius is 73.554 +/- 19.687 deg (3 sigma). The annulus is consistent with the Fermi-GBM ground position (glg_loclist_all_bn170817529_v01.txt). This annulus may be improved. A triangulation map is posted at http://www.ioffe.ru/LEA/GRBs/GRB170817_T45666/IPN/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21516 SUBJECT: LIGO/Virgo G298048: Potential host galaxies from the GLADE catalog DATE: 17/08/17 18:55:12 GMT FROM: Gergely Dalya at Eotvos U Gergely Dlya, Bence Bcsy and Peter Raffai (Eotvos U) reports on behalf of the GLADE team: We have found 15 galaxies in the GLADE catalog [1], within the 1 sigma GW localisation area reported by the LVC in GCN 21513, and within 40 +/- 8 Mpc distance limits. We used the localisation information obtained using data from H1, L1, and V1, without making any assumption on the orientation of the system (where the glitch coincident with the event in L1 have been removed in the analysis). The galaxies found are given in the following table, sorted based on their absolute B magnitudes (a proxy for BNS formation). All distances are luminosity distances. Note that there are 83 and 184 galaxies (not listed here) within a 50 Mpc distance limit, inside the 2 and 3 sigma localisation areas, respectively. RA[deg] Dec[deg] Distance [Mpc] app. B mag abs. B mag --------------------------------------------------------------------------- 194.366257 -19.691298 44.75 12.68 -20.574 196.89064 -24.008606 43.944 12.68 -20.5345 193.998657 -19.26899 41.944 13.27 -19.8433 197.018005 -23.796844 34.097 12.87 -19.7936 196.735474 -23.91707 33.653 13.07 -19.5651 196.774902 -23.67704 33.42 13.18 -19.44 196.907242 -23.57892 41.75 14.21 -18.8933 196.600052 -24.164007 33.431 13.78 -18.8407 196.907013 -23.938364 45.986 15.59 -17.7231 196.580811 -22.98033 39.361 15.71 -17.2653 194.55 -21.04596 41.778 15.96 -17.1447 196.348 -23.52258 39.583 16.1 -16.8875 196.354 -23.5025 43.583 16.88 -16.3166 196.892 -23.8152 42.855 17.4 -15.76 196.063 -22.8812 39.083 17.54 -15.4199 --------------------------------------------------------------------------- The total B luminosity of candidate galaxies exceeds by a factor of 4.5 the total B luminosity we would expect for the error volume from the average B luminosity of the local universe determined by Kopparapu et al. [2]. Based on this we assume that in fact the completeness of our galaxy sample within the volume is 100% in terms of integrated B luminosity. We have independently found 29 galaxies in the GLADE catalog within 40 +/- 8 Mpc distance limits, residing in the +/- 5 degree neighborhood of the IceCube neutrino candidate with Fermi GBM trigger 524666471/170817529 reported by Bartos et al. in GCN 21511. The galaxies found are given in the following table, sorted based on their absolute B magnitudes (a proxy for BNS formation). All distances are luminosity distances. RA[deg] Dec[deg] Distance [Mpc] app. B mag abs. B mag --------------------------------------------------------------------------- 177.21 -2.03229 40.365 13.00 -20.03 178.604523 -2.319723 41.306 13.79 -19.2901 178.419342 -3.996517 33.500 13.406 -19.2192 185.141 0.7882 33.153 13.77 -18.8326 185.274 0.55284 33.569 14.85 -17.7797 178.441 -8.01641 33.819 15.14 -17.5058 177.76 -4.08201 45.681 15.90 -17.3987 185.798 -3.49124 46.833 16.27 -17.0828 178.811 -6.45435 34.361 15.85 -16.8303 178.798 0.48769 46.990 16.69 -16.67 178.428 -1.65985 45.597 16.72 -16.5747 177.022 0.99129 43.194 16.96 -16.2171 178.548 -1.13135 45.75 17.12 -16.182 181.052 0.80256 41.236 17.02 -16.0564 185.169 -3.53346 45.708 17.58 -15.72 178.568 -4.63232 45.722 17.88 -15.4206 178.573 -4.02153 35.764 17.83 -14.9372 186.574 1.74166 34.806 17.81 -14.8983 185.791 0.4271 33.986 18.11 -14.5465 184.184 -2.8103 45.958 18.81 -14.5018 177.695 -3.2618 40.375 18.69 -14.3406 181.28 -0.11052 34.833 18.38 -14.33 180.632 -2.3032 40.083 18.71 -14.3048 178.049 0.74188 35.667 18.53 -14.2313 183.412 -1.29349 34.278 18.55 -14.1251 186.332 -1.599 34.833 18.77 -13.94 183.066 -0.56531 32.333 18.61 -13.9382 180.104 -4.9137 35.736 19.09 -13.6755 183.379 1.42761 42.8549 19.64 -13.52 --------------------------------------------------------------------------- [1] GLADE website: http://aquarius.elte.hu/glade/ [2] Kopparapu, R. K., Hanna, C., Kalogera, V., et al. 2008, ApJ, 675, 1459 //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21518 SUBJECT: LIGO/Virgo G298048: Insight-HXMT observations DATE: 17/08/17 19:35:28 GMT FROM: Shaolin Xiong at IHEP J. Y. Liao, C. K. Li, M. Y. Ge, Y. Huang, Z. W. Li, S. L. Xiong, Y. Liu, C. Z. Liu, X. F. Li, Z. Chang, X. F. Lu, J. L. Zhao, A. M. Zhang, Y. F. Zhang, C. L. Zou (IHEP), Y. J. Jin, Z. Zhang (THU), T. P. Li (IHEP/THU), F. J. Lu, L. M. Song, H. Y. Wang, M. Wu, Y. P. Xu, S. N. Zhang (IHEP), report on behalf of the Insight-HXMT team: Insight-HXMT was taking data normally around the GBM trigger time (T0=2017-08-17 12:41:06.47 UTC) of the short weak bn170817529 (Connaughton 2017, GCN 21506), which is about 2 seconds after the LIGO trigger of G298048 reported in GCN 21505. This GRB was also detected by the INTEGRAL/SPI-ACS (Savchenko 2017, GCN 21507). At T0, both the GBM localization error region and the LHV location area (reported in GCN 21513) were fully covered by Insight-HXMT without occultation by the Earth. The incident angle is about 30 deg for the best GBM location (Ra=190.76 deg, Dec=-39.43 deg), corresponding to almost the optimum sensitivity of Insight-HXMT to a GRB. Within T0 +/- 1000 s, no significant excess (SNR > 5) was found in a search of the Insight-HXMT raw light curves with time scales of 20 ms, 50 ms, 0.2 s and 1 s, respectively. A 3.2 sigma excess is found 2 s before T0, however, consistent with background fluctuations. With the three typical GRB Band spectral models, integration time of 1 s and the best GBM localization, the 3-sigma upper-limits of fluence (0.2 - 5 MeV, incident energy) are reported below: Band model 1 (alpha=-1.9, beta=-3.7, Ep=70 keV): 1.04e-07 erg cm^-2 Band model 2 (alpha=-1.0, beta=-2.3, Ep=230 keV): 1.44e-07 erg cm^-2 Band model 3 (alpha=0.0, beta=-1.5, Ep=1000 keV): 2.22e-07 erg cm^-2 All measurements above are made with the CsI detectors operating in the regular mode with the energy range of about 80-800 keV (record energy). Only gamma-rays with energy greater than about 200 keV can penetrate the spacecraft and leave signals in the CsI detectors installed inside of the telescope. The analysis results presented above are preliminary; more analysis results with refined LIGO locations will be reported later. In addition, Insight-HXMT has initiated a ToO observation to the GBM location region. ToO observation results will be reported as well. Insight-HXMT is the first Chinese space X-ray telescope, which was funded jointly by the China National Space Administration (CNSA) and the Chinese Academy of Sciences (CAS). More information about it could be found at: http://www.hxmt.org/index.php/enhome . //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21519 SUBJECT: LIGO/Virgo G298048: Nearby Galaxies in the Localization Volume DATE: 17/08/17 20:00:07 GMT FROM: Mansi M. Kasliwal at Caltech David O. Cook (Caltech), Angela Van Sistine (UW Milwaukee), Leo Singer (NASA/GSFC), and M. M. Kasliwal (Caltech) report on behalf of the GROWTH (Global Relay of Observatories Watching Transients Happen) collaborations We spatially cross-matched the LIGO/Virgo G298048 trigger (90% containment volume using bayestar-HLV.fits; LVC GCN 21513) with our Census of the Local Universe (CLU; Cook et al. in prep) galaxy catalog and found 54 galaxies. This catalog is a compilation of galaxies with existing redshifts from many sources (e.g., NED, SDSS, etc) and new galaxies from a 3PI four-filter narrow-band survey to look for redshifted Halpha emission out to 200 Mpc with the Palomar Oschin 48-inch telescope. The narrow-band survey is limited to a declination above -20 degrees, thus all galaxies within the 90% volume come from the compiled CLU catalog with no Halpha overlap. We list here all 54 galaxies sorted by stellar mass (Mstar) for galaxies whose location on the sky and distance falls in the 90% volume reported by the BAYESTAR probability sky map (Singer et al. 2016). We also list the dust-corrected star formation rates (SFRs) for galaxies with GALEX FUV detections and a 'nan' for those with no detection. In addition, we have cross-matched the CLU catalog with the IceCube source closest to the LIGO localization (GCN #21511) and found 1 galaxy in the quoted error circle (ra=182.0 deg; dec=-3.2 deg; radius=0.9 deg) and a distance less than 50 Mpc. This galaxy in presented at the bottom of the table below and is marked by '**'. Finally, we have compared CLU to the GLADE results posted in the GCN #21516 and found that all 15 galaxies reported by GLADE are a subset of our 54 galaxies in the 90% LIGO volume. The matched galaxies are marked by '*' name_NED ra dec distmpc logsfr_fuv logmstar dm_kin P ----------------------------------------- -------- -------- ------- ---------- -------- ------ -------------- NGC 4970 196.8906 -24.0086 46.50 nan 10.42 33.34 0.67982512378* NGC 4830 194.3663 -19.6913 47.90 -1.419 10.41 33.40 0.751692025898* NGC 4993 197.4487 -23.3839 41.66 nan 10.26 33.10 0.406381229308 NGC 4968 196.7749 -23.6770 42.24 0.626 10.25 33.13 0.505916529441* IC 4197 197.0180 -23.7969 43.24 nan 10.24 33.18 0.484445523125* IC 4180 196.7354 -23.9171 42.46 -0.623 10.17 33.14 0.601966463045* ESO 508- G 033 199.0969 -26.5614 45.59 0.199 9.95 33.29 0.825983269095 MCG -02-33-036 193.1066 -15.5172 53.87 -1.130 9.86 33.66 0.877644438005 ESO 508- G 010 196.9080 -23.5790 43.04 nan 9.51 33.17 0.437793300499* MCG -03-33-023 194.2521 -17.3202 56.79 nan 9.33 33.77 0.896518620494 ESO 575- G 053 196.2705 -22.3839 36.37 -0.856 9.33 32.80 0.22864531721 2MASX J12525109-1529300 193.2130 -15.4916 52.26 nan 9.31 33.59 0.840364529116 2MASX J12505229-1454238 192.7180 -14.9066 52.96 -0.855 9.29 33.62 0.887842401044 2MASX J12573271-1942006 194.3863 -19.7002 52.39 -1.788 9.25 33.60 0.869507751703 ESO 576- G 003 197.6488 -21.7482 42.04 nan 9.18 33.12 0.892767805914 UGCA 331 197.6914 -23.8657 40.82 nan 9.17 33.05 0.46533406188 IC 3825 192.6544 -14.4828 51.04 -0.985 9.17 33.54 0.869690712974 ESO 575- G 055 196.6663 -22.4561 44.49 -0.975 9.07 33.24 0.318944282323 ESO 508- G 003 196.6000 -24.1641 40.52 nan 9.06 33.04 0.725785234193* ESO 508- G 019 197.4663 -24.2391 41.79 nan 8.98 33.11 0.468015512935 ESO 575- G 029 193.9986 -19.2691 45.21 nan 8.96 33.28 0.776285954276* 2MASX J13073768-2356181 196.9071 -23.9384 49.73 nan 8.92 33.48 0.75425858513* 2MFGC 10461 197.1774 -23.7756 41.39 nan 8.90 33.08 0.402195426608 2MASX J13061939-2258491 196.5805 -22.9804 41.51 -1.129 8.83 33.09 0.348727829094* UGCA 327 196.9370 -22.8579 37.29 nan 8.81 32.86 0.24221860665 GALEXASC J125520.46-170546.9 193.8364 -17.0966 56.69 -1.151 8.67 33.77 0.893717974236 WINGS J125412.84-153523.6 193.5534 -15.5899 50.96 nan 8.64 33.54 0.819574163679 ESO 508- G 004 196.7177 -22.8405 41.37 -1.063 8.61 33.08 0.261954420028 ESO 508- G 014 197.1342 -23.3469 46.61 -1.525 8.60 33.34 0.502436701005 6dF J1254495-160308 193.7063 -16.0523 48.02 nan 8.52 33.41 0.63989406271 GALEXASC J125811.97-210246.3 194.5501 -21.0461 43.89 -1.349 8.47 33.21 0.896108050802* GALEXASC J130525.30-233008.8 196.3546 -23.5025 45.90 -1.011 8.43 33.31 0.758188818845 GALEXASC J125259.36-152150.9 193.2474 -15.3639 49.87 -1.321 8.41 33.49 0.780610774955 GALEXASC J125301.39-151007.7 193.2552 -15.1693 53.40 -1.700 8.35 33.64 0.897732213223 GALEXASC J130707.37-240634.4 196.7822 -24.1104 41.50 nan 8.30 33.09 0.649957568967 6dF J1305235-233121 196.3478 -23.5224 41.71 nan 8.28 33.10 0.683125977193* GALEXASC J130415.26-225251.3 196.0633 -22.8814 41.23 -1.577 8.20 33.08 0.569226109088* 6dF J1309177-242256 197.3241 -24.3821 40.36 nan 8.12 33.03 0.493271503844 UGCA 328 197.3298 -24.3866 41.03 nan 8.11 33.07 0.501078476114 GALEXASC J125157.02-160617.8 192.9872 -16.1047 50.30 nan 8.06 33.51 0.758957103398 ESO 508- G 035 199.4497 -26.9025 37.77 -1.526 8.02 32.89 0.845327686458 GALEXASC J130918.58-242304.8 197.3286 -24.3846 39.81 nan 7.98 33.00 0.48826441659 ABELL 1664_11:[PSE2006] 2506 196.8922 -23.8153 42.80 nan 7.93 33.16 0.503854909981* GALEXASC J131426.62-271242.6 198.6106 -27.2120 29.32 -1.784 7.82 32.34 0.889086337352 ABELL 1631:[CZ2003]B0295[024] 192.8695 -15.8723 53.56 nan 7.77 33.64 0.872555532297 WINGS J125701.38-172325.2 194.2558 -17.3903 26.13 nan 7.10 32.09 0.266736706214 HDCE 0763 196.9733 -23.7569 43.09 nan nan 33.17 0.48258630738 ESO 508 197.1336 -23.6224 45.66 nan nan 33.30 0.492829108028 [TSK2008] 0073 197.7951 -23.5882 40.44 nan nan 33.03 0.532282847671 USGC S204 196.9600 -23.5400 41.72 nan nan 33.10 0.382686501893 [TSK2008] 0052 199.0736 -27.6878 29.69 nan nan 32.36 0.894365407375 HIPASS J1255-15 193.8983 -15.0175 27.32 nan nan 32.18 0.834811408702 2MFGC 10484 197.4617 -24.2419 42.31 nan nan 33.13 0.47821726929 UGCA 325 196.7796 -24.1119 42.70 nan nan 33.15 0.668934329707 GALEXASC J120652.88-040236.6 181.7196 -04.0437 27.17 nan 7.34 32.17 N/A*** **Galaxy found within the IceCube localization closest to the LIGO localization in the GCN #21511. * Galaxies matched to the GLADE catalog reported in GCN #21516 The SFRs are derived from GALEX all sky kron FUV magnitudes via the prescription of Murphy et al. (2011) and have been corrected for internal dust extinction using a combination of GALEX FUV and 22um ALLWISE fluxes (Hao et al. 2011). The quoted stellar masses are derived from 3.4um ALLWISE fluxes and a mass-to-light ratio of 0.5 (McGaugh & Schombert et al. 2015). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21521 SUBJECT: LIGO/Virgo G298048: Nearby Galaxies in the Localization Volume with Face-on Assumption DATE: 17/08/17 20:12:41 GMT FROM: Mansi M. Kasliwal at Caltech David O. Cook (Caltech), Angela Van Sistine (UW Milwaukee), Leo Singer (NASA/GSFC), and M. M. Kasliwal (Caltech) report on behalf of the GROWTH (Global Relay of Observatories Watching Transients Happen) collaboration We spatially cross-matched the LIGO/Virgo G298048 trigger with the assumption of face-on orientation (90% containment volume using bayestar-HLV-face-on.fits; LVC GCN 21513) with our Census of the Local Universe (CLU; Cook et al. in prep) galaxy catalog and found 13 galaxies. This catalog is a compilation of galaxies with existing redshifts from many sources (e.g., NED, SDSS, etc) and new galaxies from a 3PI four-filter narrow-band survey to look for redshifted Halpha emission out to 200 Mpc with the Palomar Oschin 48-inch telescope. The narrow-band survey is limited to a declination above -20 degrees, thus all galaxies within the 90% volume come from the compiled CLU catalog with no Halpha overlap. We list here all 13 galaxies sorted by stellar mass (Mstar) for galaxies whose location on the sky and distance falls in the 90% volume reported by the BAYESTAR probability sky map (Singer et al. 2016). We also list the dust-corrected star formation rates (SFRs) for galaxies with GALEX FUV detections and a 'nan' for those with no detection. Of the 13 galaxies, 4 galaxies are not in the list of 54 galaxies reported in GCN #21519 without the face-on assumption. The new galaxies are marked with a ‘*’. name_NED ra dec distmpc logsfr_fuv logmstar dm_kin P ----------------------------------------- -------- -------- ------- ---------- -------- ------ -------------- NGC 4830 194.3663 -19.6913 47.90 -1.419 10.41 33.40 0.600362551579 MCG -04-31-042 198.5739 -26.5827 54.70 nan 9.98 33.69 0.820306676922* 2MASX J12525109-1529300 193.2130 -15.4916 52.26 nan 9.31 33.59 0.807651962502 2MASX J12573271-1942006 194.3863 -19.7002 52.39 -1.788 9.25 33.60 0.723692228565 2MASX J12551928-1456593 193.8304 -14.9499 48.56 nan 9.22 33.43 0.801217259508* IC 3825 192.6544 -14.4828 51.04 -0.985 9.17 33.54 0.776579689512 2MASX J13073768-2356181 196.9071 -23.9384 49.73 nan 8.92 33.48 0.634606246205 WINGS J125412.84-153523.6 193.5534 -15.5899 50.96 nan 8.64 33.54 0.595385148382 6dF J1254495-160308 193.7063 -16.0523 48.02 nan 8.52 33.41 0.197814505144 GALEXASC J125259.36-152150.9 193.2474 -15.3639 49.87 -1.321 8.41 33.49 0.419676266799 GALEXASC J125157.02-160617.8 192.9872 -16.1047 50.30 nan 8.06 33.51 0.410982650697 GALEXASC J125404.25-145044.4 193.5173 -14.8457 50.85 -1.659 7.75 33.53 0.823290805821* MCG -02-33-014 192.3380 -13.3512 49.57 nan nan 33.48 0.82251638918* * Galaxies not reported in the CLU crossmatch to LIGO with no orientation assumptions (GCN #21519). The SFRs are derived from GALEX all sky kron FUV magnitudes via the prescription of Murphy et al. (2011) and have been corrected for internal dust extinction using a combination of GALEX FUV and 22um ALLWISE fluxes (Hao et al. 2011). The quoted stellar masses are derived from 3.4um ALLWISE fluxes and a mass-to-light ratio of 0.5 (McGaugh & Schombert et al. 2015). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21522 SUBJECT: LIGO/Virgo G298048 ANTARES search DATE: 17/08/17 20:35:31 GMT FROM: Damien Dornic at CPPM/CNRS M. Ageron (CPPM/CNRS), B. Baret (APC/CNRS), A. Coleiro (IFIC & APC), D. Dornic (CPPM/CNRS), A. Kouchner (APC/Universite Paris Diderot), T. Pradier (IPHC/Universite de Strasbourg) report on behalf of the ANTARES Collaboration: Using on-line data from the ANTARES detector, we have performed a follow-up analysis of the recently reported LIGO/Virgo G298048 event using the updated Bayestar-HLV probability map at event time. The ANTARES visibility at the time of the alert together with the 90% contour of the probability map are shown in: https://www.cppm.in2p3.fr/~dornic/events/G298048/170817_visi2.png (gwantares/GW@ANT31). The 90% contour of the probability map is outside of the ANTARES field-of-view at the alert time. No up-going muon neutrino candidate events were recorded in the ANTARES sky during a +/- 500s time-window centered on the G298048 event time. The expected number of atmospheric background events in the region visible by ANTARES is ~1.1e-2 in the +/- 500s time window. An extended search during +/- 1 hour gives no up-going neutrino coincidence. An estimate of the upper limit on the associated neutrino fluence will be sent in a subsequent circular. ANTARES, being installed in the Mediterranean Deep Sea, is the largest neutrino detector in the Northern Hemisphere. It is primarily sensitive to astrophysical neutrinos in the TeV-PeV energy range. At 10 TeV, the median angular resolution for muon neutrinos is below 0.5 degrees. In the range 1-100 TeV, ANTARES has the best sensitivity to a large fraction of the Southern sky. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21524 SUBJECT: LIGO/Virgo G298048: Swift/BAT data search DATE: 17/08/17 21:34:36 GMT FROM: Amy Lien at GSFC/Swift S. D. Barthelmy (NASA/GSFC), A. Y. Lien (GSFC/UMBC), D. M. Palmer (LANL), T. Sakamoto (AGU), A. A. Breeveld (MSSL-UCL), A. P. Beardmore (U. Leicester), D. N. Burrows (PSU), S. Campana (INAF-OAB), S. B. Cenko (NASA/GSFC), G. Cusumano (INAF-IASF PA), A. D'Ai (INAF-IASFPA), P. D'Avanzo (INAF-OAB), V. D'Elia(ASDC), S. Emery (UCL-MSSL), P. A. Evans (U. Leicester), P. Giommi (ASI), C. Gronwall (PSU), J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA), N. P. M. Kuin (UCL-MSSL), F. E. Marshall (NASA/GSFC), A. Melandri (INAF-OAB), B. Mingo (U. Leicester), J. A. Nousek (PSU), S. R. Oates (Uni. of Warwick), P. T. O'Brien (U. Leicester), J. P. Osborne (U. Leicester), C. Pagani (U. Leicester), K. L. Page (U.Leicester), M. Perri (ASDC), J. L. Racusin (NASA/GSFC), B. Sbarufatti (INAF-OAB/PSU), M. H. Siegel (PSU), G. Tagliaferri (INAF-OAB), E. Troja (NASA/GSFC/UMCP) report on behalf of the Swift team: We report the search results in the BAT data within T0 +/- 100 s of the LVC event G298048 (LIGO/VIRGO Collaboration GCN Circ. 21513), where T0 is the LVC trigger time (2017-08-17T12:41:04.445 UTC). The center of the BAT FOV at T0 is RA = 36.075 deg, DEC = -52.287 deg, ROLL = 108.515 deg. The BAT Field of View (>10% partial coding) covers 0.0% of the integrated LVC localization probability. That is, there is no overlap between the BAT field of view and the LVC probability region at T0. Within T0 +/- 100 s, no significant detections (signal-to-noise ratio >~ 5 sigma) are found in the BAT raw light curves with time bins of 64 ms, 1 s, and 1.6 s, respectively. Assuming an on-axis (100% coded) short GRB with a typical spectrum in the BAT energy range (i.e., a simple power-law model with a power-law index of -1.32, Lien & Sakamoto et al. 2016), the 5-sigma upper limit in the 1-s binned light curve corresponds to a flux upper limit (15-350 keV) of ~ 7.82 x 10^-8 erg/s/cm^2. BAT retains decreased, but significant, sensitivity to rate increases for gamma-ray events outside of its FOV. About 0.15% of the integrated LVC localization probability was outside of the BAT FOV but above the Earth's limb from Swift's location, and the corresponding flux upper limits for this region are within roughly an order of magnitude of those within the FOV. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21525 SUBJECT: LIGO/Virgo G298048: AGILE MCAL observations DATE: 17/08/17 22:01:26 GMT FROM: Francesco Verrecchia at ASDC, INAF-OAR M. Pilia (INAF/OA-Cagliari), M. Cardillo, G. Piano (INAF/IAPS), M. Tavani (INAF/IAPS, and Univ. Roma Tor Vergata) F. Verrecchia (SSDC and INAF/OAR), A. Bulgarelli (INAF/IASF-Bo), C. Pittori (SSDC and INAF/OAR), I. Donnarumma (ASI), F. Longo (Univ. Trieste and INFN Trieste), A. Ursi, G. Minervini, A. Argan, Y. Evangelista (INAF/IAPS), F. Lucarelli (SSDC and INAF/OAR), N. Parmiggiani, A. Zoli, V. Fioretti, F. Fuschino (INAF/IASF-Bo), A. Trois (INAF/OA-Cagliari) M. Marisaldi (INAF/IASF-Bo and Bergen University), A. Giuliani (INAF/IASF-Mi), report on behalf of the AGILE Team: In response to the LIGO/Virgo GW event G298048 at T0 = 2017-08-17 12:41:04.446 UTC, a preliminary analysis of the AGILE MiniCALorimeter (MCAL) data found no event candidates within a time interval covering approximately -/+ 10 sec from the LIGO T0. Due to Earth occultation the MCAL field of view did not cover the new revised HLV G298048 90% localization region (GCN #21513). At T0 MCAL exposed about 10% of the Fermi-GBM 3-sigma localization region (GCN #21506, T0_GBM=2017-08-17T12:41:06.47 UTC) . The closest in time MCAL triggered data acquisition occurred about 7 sec after the Fermi-GBM trigger, resulting in typical values of the fluence 3-sigma UL ranging from 5.2 e^-7 erg cm^-2 to 6.3 e^-7 erg cm^-2 (assuming a power law spectral model with photon index1.4 and 1 sec integration time). The AGILE-MCAL detector is a CsI detector with a 4-pi FoV, working in the range 0.4 - 100 MeV. Additional analysis of AGILE data is in progress. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21526 SUBJECT: LIGO/Virgo G298048: AGILE GRID observations DATE: 17/08/17 22:22:43 GMT FROM: Francesco Verrecchia at ASDC, INAF-OAR G. Piano (INAF/IAPS), F. Verrecchia (SSDC and INAF/OAR), M. Pilia (INAF/OA-Cagliari), M. Cardillo (INAF/IAPS), M. Tavani (INAF/IAPS, and Univ. Roma Tor Vergata), A. Bulgarelli (INAF/IASF-Bo), C. Pittori (SSDC and INAF/OAR), I. Donnarumma (ASI), F. Longo (Univ. Trieste and INFN Trieste), A. Ursi, G. Minervini, A. Argan, Y. Evangelista (INAF/IAPS), F. Lucarelli (SSDC and INAF/OAR), N. Parmiggiani, A. Zoli, V. Fioretti, F. Fuschino (INAF/IASF-Bo), A. Trois (INAF/OA-Cagliari) M. Marisaldi (INAF/IASF-Bo and Bergen University), A. Giuliani (INAF/IASF-Mi), report on behalf of the AGILE Team: In response to the LIGO/Virgo GW trigger event G298048 at T0 = 2017-08-17 12:41:04.446 UTC (GCN #21505) and the Fermi-GBM trigger event 170817.529 at T1 = 12:41:06.470 UTC (GCN #21506), we performed an analysis of the AGILE Gamma-Ray Imaging Detector (GRID) data on different timescales. On Fermi-GBM trigger time (T1) the GRID exposure covered nearly 10% of the Fermi-GBM 3-sigma localization region, observed at off-axis angles between 15 and 55 deg. Due to Earth occultation the GRID field of view did not cover the new revised HLV G298048 90% localization region (GCN #21513). An analysis of the data in the energy range 50 MeV - 10 GeV was performed on timescales from 2 to 100 sec centered at T1. Preliminary values of 3-sigma upper limits (UL) obtained within the accessible Fermi-GBM 3-sigma localization region are reported below: from 1.4e-06 to 2.2e-06 erg cm^-2 s^-1 for integration time of 2s from 1.4e-07 to 6.6e-07 erg cm^-2 s^-1 for integration time of 20s from 3.2e-08 to 8.8e-08 erg cm^-2 s^-1 for integration time of 100s These measurements were obtained with AGILE observing a large portion of the sky in spinning mode. Additional analysis of AGILE data is in progress. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21527 SUBJECT: LIGO/Virgo G298048: Updated sky map from gravitational-wave data DATE: 17/08/17 23:54:40 GMT FROM: Reed Clasey Essick at MIT The LIGO Scientific Collaboration and the Virgo Collaboration report: Parameter estimation has been performed using LALInference (Veitch et al., PRD 91, 042003) and a revised sky map, preliminary-LALInference.fits.gz, is available for retrieval from the GraceDB event page: https://gracedb.ligo.org/events/G298048 We caution that this is a preliminary map from the offline parameter estimation. This analysis uses data from the LIGO Hanford, LIGO Livingston, and Virgo detectors with the noise transient in Livingston removed from the data prior to the analysis, as described in GCN 21513. Posterior chains in the parameter estimation may not yet have fully converged. The 50% and 90% credible regions span about 8.6 and 33.6 square degrees, respectively, which are somewhat larger than the initial BAYESTAR sky map. The centroid (maximum a posteriori) sky location is R.A.=13h09m, Dec.=-25d37m. We will continue to refine the sky map as offline parameter estimation improves and as we apply additional methods of cleaning the data. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21528 SUBJECT: LIGO/Virgo G298048 - Update on Fermi/GBM GRB 170817A Analysis DATE: 17/08/18 00:36:12 GMT FROM: Adam Goldstein at Fermi/GBM A. Goldstein (USRA), P. Veres (UAH), and A. von Kienlin (MPE) report on behalf of the GBM-LIGO Group: L. Blackburn (CfA), M. S. Briggs (UAH), J. Broida (Carleton College), E. Burns (NASA/GSFC), J. Camp (NASA/GSFC), T. Dal Canton (NASA/GSFC), N. Christensen (Carleton College), V. Connaughton (USRA), R. Hamburg (UAH), C. M. Hui (NASA/MSFC), P. Jenke (UAH), D. Kocevski (NASA/MSFC), N. Leroy (LAL), T. Littenberg (NASA/MSFC), J. McEnery (NASA/GSFC), R. Preece (UAH), J. Racusin (NASA/GSFC), P. Shawhan (UMD), K. Siellez (GATech), L. Singer (NASA/GSFC), J. Veitch (Glasgow), C. Wilson-Hodge (NASA/MSFC) The GBM trigger (Connaughton et al., LVC GCN 21506), which we determine to be a short GRB, occurred about 2 minutes before Fermi entered the South Atlantic Anomaly. To estimate the False Alarm Rate (FAR) of a chance coincident short GRB without using spatial information, we estimate the rate of short GRBs (defined as t90 <= 2 s) triggered by GBM. GBM has a total of 351 triggered short GRBs over an estimated triggering livetime of 3.23e8 s. This results in a FAR of one per 10.7 days. A simple estimate of the False Alarm Probability using only the temporal information of the two signals is 2.2e-6 (~4.5 sigma). The initial public report of the GRB (von Kienlin et al., GCN 21520) contained the spectral information using the maximum of the GBM localization posterior. Using the maximum of the updated LIGO/Virgo localization posterior (LVC, LVC GCN 21513), which is consistent with the GBM localization, we report the updated preliminary spectral information. The estimated GRB duration is ~ 2 s and is best fit by a power-law function with an exponential high-energy cutoff from T0-0.75 to T0+1.25 s. The power-law index is -0.88 +/- 0.44 and the cutoff energy, parametrized as Epeak, is 128.0 +/- 48.7 keV. The event fluence (10-1000 keV) in this time interval is (2.2 +/- 0.5)e-7 erg/cm^2, which we estimate to be near the 58th percentile of GBM-triggered short GRB fluences. The 64 ms peak photon flux estimated starting at T0 is 3.6 +/- 1.1 ph/s/cm^2 (10-1000 keV). The corresponding spectrum over this peak flux interval is fit by an exponential high-energy power law with index = -0.29 +/- 1.01 and Epeak = 124.2 +/- 52.6 keV. The event peak energy flux (10-1000 keV) is (7.3 +/- 2.4)e-7 erg/s/cm^2. Using this spectral information and the distance information provided by the LVC (40 +/- 8 Mpc) we estimate that the isotropic energy release in gamma-rays, Eiso ~ 4.3e46 erg in the 1 keV-10 MeV energy range and the isotropic peak luminosity, Liso ~1.4e47 erg/s. These results are preliminary and may be updated with further analysis. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21529 SUBJECT: LIGO/Virgo G298048: Potential optical counterpart discovered by Swope telescope DATE: 17/08/18 01:05:23 GMT FROM: Edo Berger at Harvard U D. A. Coulter, C. D. Kilpatrick, M. R. Siebert, R. J. Foley (UCSC), B. J. Shappee, M. R. Drout, J. S. Simon, A. L. Piro (Carnegie), and A. Rest (STScI) report on behalf of the One-Meter Two-Hemisphere (1M2H) collaboration: On 2017 Aug 18 UT in the process of observing several galaxies coincident with the highest-likelihood localization region for the LIGO/Virgo G298048 trigger (LVC GCNs 21509, 21513) with the 1-m Swope telescope at Las Campanas Observatory, we detect a source 5.3 E and 8.8 N of NGC 4993, an S0 galaxy in the NGC 4993 / ESO 508-G018 group at a distance of ~40 Mpc (Tully-Fisher distance to the group; Freedman et al., ApJ, 553, 47, 2001). The object is: SSS17a 13:09:48.089 -23:22:53.35 and had a brightness of i = 16.0 mag. We have checked the minor planet center and previous SN discoveries, and have found no cross-matches. This source could possibly be optical emission associated with the LIGO/Virgo G298048 trigger. Spectroscopic observations are under way. Additional photometry has been obtained and is being analyzed. Additional observations are encouraged. The contact person for this circular is Ryan Foley (foley@ucsc.edu). [GCN OPS NOTE(28sep17): Per a combination of requests and editorial policy: (1) AR was added to the author list. (2) The contact-name sentence was added. The editor notes that RF was having sign-up problems with the LV-EM Forum and E.Berger offered to submit in his place since publication latency was important. (3) And the EB signature block was removed.] //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21530 SUBJECT: LIGO/Virgo G298048: DECam optical candidate DATE: 17/08/18 01:15:01 GMT FROM: Ryan Chornock at Ohio U S. Allam (Fermilab), J. Annis (Fermilab), E. Berger (Harvard), D. J. Brout (UPenn), D. Brown (Syracuse), R. E. Butler (Fermilab), H.-Y. Chen (Harvard), R. Chornock (Ohio University), E. Cook (TAMU), P. Cowperthwaite (Harvard), H. T. Diehl (Fermilab), A. Drlica-Wagner (Fermilab), M. R. Drout (Carnegie), R. J. Foley (UCSC), W. Fong (Northwestern), D. Fox (Penn State), J. Frieman (Fermilab/UChicago), R. Gruendl (NCSA), K. Herner (Fermilab), D. Holz (UChicago), R. Kessler (UChicago), R. Margutti (Northwestern), J. Marshall (TAMU), E. Neilsen (Fermilab), M. Nicholl (Harvard), F. Paz-Chincon (NCSA), A. Rest (STScI), M. Sako (UPenn), D. Scolnic (U Chicago), N. Smith (Arizona), M. Soares-Santos (BrandeisU), D. Tucker (Fermilab), V. A. Villar (Harvard), P. K. G. Williams (Harvard), B. Yanny (Fermilab) On behalf of the larger DESGW+community team: We have imaged the BAYESTAR localization map of LIGO/Virgo G298048 (GCN 21513) using DECam on the CTIO 4m in both i and z band. Visual inspection of unprocessed DECam images reveals a new source not present in Pan-STARRS 3Pi images north and east of NGC 4993 (d~40 Mpc, from NED), consistent with the source found by Coulter et al. (LVC GCN 21529). Analysis and further observations are ongoing. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21531 SUBJECT: LIGO/Virgo G298048: DLT40 optical candidate DATE: 17/08/18 01:41:13 GMT FROM: Stefano Valenti at UC Davis Sheng Yang (INAF-OAPd, UC Davis), Stefano Valenti(UC Davis), David Sand (UA), Leonardo Tartaglia (UA, UC Davis), Enrico Cappellaro(INAF-OAPd), Dan Reichart, Josh Haislip Vladimir Kouprianov (UNC) We report the discovery of DLT17ck. The object was discovered on 2017-08-17.99 UT at R~17.3 mag, during the ongoing D<40 Mpc (DLT40) one day cadence supernova search, using data from the PROMPT 5 0.41m telescope located at CTIO. A confirmation image was obtained on 2017-08-18.02 UT with the PROMPT telescope. DLT17ck is located at RA: 13:09:48.09 Dec: -23:22:53.4.6, 5.37 W, 8.60 S arcsec offset from the center of the host galaxy, NGC 4993, consistent with the source found by Coulter et al. (LVC GCN 21529). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21532 SUBJECT: LIGO/Virgo G298048: REM optical/NIR observations of candidate in NGC 4993 DATE: 17/08/18 02:00:40 GMT FROM: Paolo D'Avanzo at INAF-OAB A. Melandri, S. Campana, S. Covino, P. D'Avanzo (INAF-OAB), G. Greco (Urbino University/INFN Firenze), M. Branchesi (GSSI), D. Fugazza, L. Amati (INAF-IASF Bo), L. A. Antonelli, (INAF-OAR), S. Ascenzi (INAF-OAR), S. Benetti (INAF-OAPD), M.T. Botticella (INAF-OAC), E. Cappellaro (INAF-OAPD), V. D'Elia (INAF-ASDC), F. Getman (INAF-OAC), A. Grado (INAF-OAC), L. Limatola (INAF-OAC), M. Lisi (INAF-OAR), L. Nicastro (INAF-IASF Bo), E. Palazzi (INAF-IAFS Bo), E. Pian (SNS-Pisa), S. Piranomonte (INAF-OAR), L. Pulone (INAF-OAR), A. Rossi (INAF-IASF Bo), G. Stratta (Urbino University/INFN Firenze), G. Tagliaferri (INAF-OAB), V. Testa (INAF-OAR), L . Tomasella (INAF-OAPD), S. Yang (INAF-OAPD), E. Brocato (INAF-OAR) on behalf of GRavitational Wave Inaf TeAm report: We carried out optical/NIR follow-up observations of the LIGO/Virgo GW trigger G298048 (LVC GCNs 21509, 21513) with the 60-cm robotic telescope REM located at the La Silla Observatory (Chile) by performing targeted observations of catalogued galaxies in the LVC skymap. The observations were carried out simultaneously in the g, r, i, z and H bands starting on 2017 Aug 18 at 23:11:29 UT. In the optical/NIR images of the galaxy NGC 4993, obtained starting from 01:29:28 UT at airmass~3, we clearly detect in all bands the optical source reported by Coulter et al. (LVC GCN 21529), Allam et al. (LVC GCN 21530) and Yang et al. (LVC GCN 21531) Further analysis and observations are ongoing. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21533 SUBJECT: LIGO/Virgo G298048: Optical Candidate Shows No Evidence for Previous Activity in Archival ASAS-SN Data DATE: 17/08/18 02:06:30 GMT FROM: Philip Cowperthwaite at Harvard U P. S. Cowperthwaite (Harvard), R. J. Foley (UCSC), E. Berger (Harvard), We investigate ASAS-SN public data at the position of the transient source SSS17a (RA = 13:09:48.09 DECL. = -23:22:53.35, Coulter et al. 2017 GCN 21529). This source is also seen in DECam observations (Chornock et al. GCN 21530) and DLT data (Yang et al. GCN 21531). We search the last 100 days of available data, finding no strong evidence for variability at this position. The most recent observation is UT = 2017-08-14.9933703 (HJD = 2457980.49073), approximately 2 days before the GW trigger. The data can be found here: https://asas-sn.osu.edu/public/light_curve/ede9a693-78be-4049-85a0-7de11bc61c3a The photometry is generated by placing an aperture at the indicated coordinates, and therefore includes light from the host galaxy. The light curve is flat with a mean magnitude of 13.45 mag with a scatter of 0.05 mag. This indicates that the transient is most likely a young source. This circular makes use of ASAS-SN public data obtained from https://asas-sn.osu.edu/ (Shappee, B. J., Prieto, J. L., Grupe, D., et al. 2014, ApJ, 788, 48; Kochanek, C. S., Shappee, B. J., Stanek, K. Z., et al. 2017, PASP, 129, 104502). [GCN OPS NOTE(18oct17): Per author's request, the last paragraph was added.] //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21534 SUBJECT: LIGO/Virgo G298048 : Fermi-LAT search for a high-energy gamma-ray counterpart DATE: 17/08/18 02:09:53 GMT FROM: Daniel Kocevski at NASA/MSFC D. Kocevski (NASA/MSFC), N. Omodei (Stanford), S. Buson (NASA/GSFC), F. Longo (University and INFN, Trieste), J. Racusin (NASA/GSFC), and G. Vianello (Stanford) report on behalf of the Fermi-LAT team: We searched data collected by the Fermi Large Area Telescope (LAT) for possible high-energy (E > 100 MeV) gamma-ray emission in spatial/temporal coincidence with the LIGO/Virgo trigger G298048 . The Fermi gamma-ray space telescope was entering the South Atlantic Anomaly (SAA) at the time of the trigger (T0 = 2017-08-17 12:41:4.444 , 524666469.444 MET). During SAA passages the LAT does not collect data due to the high charged particle background in this region. We note that the SAA boundary employed by the LAT encompasses a larger area than the boundaries used by the the Gamma-ray Burst Monitor (GBM), resulting in different times at which the two instruments do not collect data. The LAT resumed data taking upon exiting the SAA at roughly T0 +1153 s, At that time 100% of the BAYESTAR sky map using data from all three gravitational-wave observatories (H1, L1, and V1) (GCN 21513) was within the LAT field of view (FOV). We performed a search for a transient counterpart within the 90% contour of the LIGO/Virgo sky map in the time window from T0 + 1153s to T0 + 2027s, corresponding to the times when the region entered and exited the LAT FOV, and no significant new sources were found. We also performed a search which adapted the time interval of the analysis to the exposure of each region of the sky. No significant candidate counterpart was detected. The Fermi-LAT point of contact for this event is Daniel Kocevski (daniel.kocevski@nasa.gov) The Fermi-LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden. Daniel Kocevski NASA Goddard Space Flight Center www.kocevski.com 510.316.3208 //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21535 SUBJECT: LIGO/Virgo G298048: Nearby Galaxies in the Localization Volume using the updated sky map computed using LALInference DATE: 17/08/18 02:48:50 GMT FROM: Mansi M. Kasliwal at Caltech David O. Cook (Caltech), Angela Van Sistine (UW Milwaukee), Leo Singer (NASA/GSFC), and M. M. Kasliwal (Caltech) report on behalf of the GROWTH (Global Relay of Observatories Watching Transients Happen) collaboration We spatially cross-matched the LIGO/Virgo G298048 trigger with no assumption on orientation (90% containment volume using preliminary-LALInference.fits; LVC GCN 21527) with our Census of the Local Universe (CLU; Cook et al. in prep) galaxy catalog and found 60 galaxies. This catalog is a compilation of galaxies with existing redshifts from many sources (e.g., NED, SDSS, etc) and new galaxies from a 3PI four-filter narrow-band survey to look for redshifted Halpha emission out to 200 Mpc with the Palomar Oschin 48-inch telescope. The narrow-band survey is limited to a declination above -20 degrees, thus all galaxies within the 90% volume come from the compiled CLU catalog with no Halpha overlap. We list here all 60 galaxies sorted by stellar mass (Mstar) for galaxies whose location on the sky and distance falls in the 90% volume reported by the BAYESTAR probability sky map (Singer et al. 2016). We also list the dust-corrected star formation rates (SFRs) for galaxies with GALEX FUV detections and a 'nan' for those with no detection. In addition, we have compared these galaxies to those reported in our original crossmatch (GCN #21519) and have found that 20 of these are new galaxies. The new galaxies are marked by '*'. We note that the host galaxy of the reported optical transient (GCNs #21529, #21530, #21531) is NGC 4993. This galaxy was #3 on our original list ranked by stellar mass (GCN #21519) and is #4 on the list below. name_NED ra dec distmpc logsfr_fuv logmstar dm_kin P ----------------------------------------- -------- -------- ------- ---------- -------- ------ --------------- NGC 5078 199.9582 -27.4102 29.51 nan 10.57 32.35 0.887513795025* NGC 4970 196.8906 -24.0086 46.50 nan 10.42 33.34 0.518705272027 NGC 4830 194.3663 -19.6913 47.90 -1.419 10.41 33.40 0.858268936834 NGC 4993 197.4487 -23.3839 41.66 nan 10.26 33.10 0.64123728367 NGC 4968 196.7749 -23.6770 42.24 0.626 10.25 33.13 0.316464198585 IC 4197 197.0180 -23.7969 43.24 nan 10.24 33.18 0.445236314135 IC 4180 196.7354 -23.9171 42.46 -0.623 10.17 33.14 0.231620854391 MCG -04-31-042 198.5739 -26.5827 54.70 nan 9.98 33.69 0.895990447512* ESO 508- G 033 199.0969 -26.5614 45.59 0.199 9.95 33.29 0.615247563764 IC 4219 199.6239 -31.6309 52.19 -0.053 9.87 33.59 0.874563970341* IC 0874 199.7522 -27.6286 30.90 nan 9.85 32.45 0.789658618241* ESO 508- G 010 196.9080 -23.5790 43.04 nan 9.51 33.17 0.481194307217 2MASX J13161781-2926415 199.0742 -29.4450 52.93 -1.230 9.40 33.62 0.784286018046* ESO 575- G 053 196.2705 -22.3839 36.37 -0.856 9.33 32.80 0.36841088215 IC 0879 199.9190 -27.4290 34.11 -0.673 9.27 32.66 0.81030188127* UGCA 331 197.6914 -23.8657 40.82 nan 9.17 33.05 0.643613070644 ESO 575- G 044 NED01 195.0910 -22.6947 35.60 nan 9.14 32.76 0.815693971686* ESO 575- G 055 196.6663 -22.4561 44.49 -0.975 9.07 33.24 0.767149920359 ESO 508- G 003 196.6000 -24.1641 40.52 nan 9.06 33.04 0.0809646816159 ESO 508- G 019 197.4663 -24.2391 41.79 nan 8.98 33.11 0.390107508863 ESO 575- G 029 193.9986 -19.2691 45.21 nan 8.96 33.28 0.856267417303 2MASX J13073768-2356181 196.9071 -23.9384 49.73 nan 8.92 33.48 0.753012347515 2MFGC 10461 197.1774 -23.7756 41.39 nan 8.90 33.08 0.413936564291 2MASX J13061939-2258491 196.5805 -22.9804 41.51 -1.129 8.83 33.09 0.459238357582 UGCA 327 196.9370 -22.8579 37.29 nan 8.81 32.86 0.610525424738 ESO 508- G 004 196.7177 -22.8405 41.37 -1.063 8.61 33.08 0.621228481694 ESO 508- G 014 197.1342 -23.3469 46.61 -1.525 8.60 33.34 0.753661507789 GALEXASC J125811.97-210246.3 194.5501 -21.0461 43.89 -1.349 8.47 33.21 0.847953733375 ESO 444- G 033 201.5178 -32.1291 31.45 -1.169 8.46 32.49 0.873767002259* GALEXASC J130525.30-233008.8 196.3546 -23.5025 45.90 -1.011 8.43 33.31 0.440966168867 GALEXASC J131109.37-280035.5 197.7891 -28.0099 28.84 nan 8.36 32.30 0.670375919006* GALEXASC J130707.37-240634.4 196.7822 -24.1104 41.50 nan 8.30 33.09 0.143978844705 6dF J1305235-233121 196.3478 -23.5224 41.71 nan 8.28 33.10 0.18957340774 GALEXASC J130415.26-225251.3 196.0633 -22.8814 41.23 -1.577 8.20 33.08 0.246973097253 6dF J1309177-242256 197.3241 -24.3821 40.36 nan 8.12 33.03 0.267382395401 UGCA 328 197.3298 -24.3866 41.03 nan 8.11 33.07 0.292373909456 ESO 443- G 079 197.5947 -27.9770 31.71 nan 8.10 32.51 0.740389521428* ESO 508- G 035 199.4497 -26.9025 37.77 -1.526 8.02 32.89 0.600958568007 GALEXASC J130918.58-242304.8 197.3286 -24.3846 39.81 nan 7.98 33.00 0.250629160585 ABELL 1664_11:[PSE2006] 2506 196.8922 -23.8153 42.80 nan 7.93 33.16 0.37496420498 AM 1316-263 199.8900 -26.8027 32.03 -2.024 7.93 32.53 0.888395580501* GALEXASC J132218.16-300914.6 200.5747 -30.1544 34.12 -1.953 7.86 32.66 0.685502037779* GALEXASC J131426.62-271242.6 198.6106 -27.2120 29.32 -1.784 7.82 32.34 0.411085021807 ESO 508- G 039 199.6006 -27.4343 28.44 -1.682 7.72 32.27 0.841960065682 ABELL 1664_13:[PSE2006] 1313 195.7757 -23.8657 22.93 nan 7.72 31.80 0.79106477475* ESO 508- G 021 197.5043 -26.7119 29.71 -1.582 7.66 32.36 0.329579404218* ESO 444- G 002 199.1892 -27.8856 23.46 -1.205 7.59 31.85 0.866962651084* GALEXASC J132014.00-300208.9 200.0584 -30.0363 22.70 -1.668 7.53 31.78 0.869946416036* GALEXASC J130430.75-241313.3 196.1277 -24.2201 20.54 -2.616 7.19 31.56 0.822744075967* WINGS J125701.38-172325.2 194.2558 -17.3903 26.13 nan 7.10 32.09 0.8626975064 GALEXASC J131007.01-263546.5 197.5292 -26.5963 28.58 -1.915 nan 32.28 0.322783340928* USGC S204 196.9600 -23.5400 41.72 nan nan 33.10 0.471831679854 UGCA 325 196.7796 -24.1119 42.70 nan nan 33.15 0.198214466434 HDCE 0763 196.9733 -23.7569 43.09 nan nan 33.17 0.429404174971 ESO 508 197.1336 -23.6224 45.66 nan nan 33.30 0.664939464108 GALEXMSC J132152.52-312233.6 200.4688 -31.3781 30.87 nan nan 32.45 0.724356348566* [TSK2008] 0052 199.0736 -27.6878 29.69 nan nan 32.36 0.593309320022 2MFGC 10484 197.4617 -24.2419 42.31 nan nan 33.13 0.411745360516 ESO 444- G 004 199.2656 -31.5891 32.65 -1.507 nan 32.57 0.873219502269* [TSK2008] 0073 197.7951 -23.5882 40.44 nan nan 33.03 0.772082721414 * Galaxies not reported in the original CLU-LIGO crossmatch (GCN #21519) The SFRs are derived from GALEX all sky kron FUV magnitudes via the prescription of Murphy et al. (2011) and have been corrected for internal dust extinction using a combination of GALEX FUV and 22um ALLWISE fluxes (Hao et al. 2011). The quoted stellar masses are derived from 3.4um ALLWISE fluxes and a mass-to-light ratio of 0.5 (McGaugh & Schombert et al. 2015). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21536 SUBJECT: LIGO/Virgo G298048: Inspection of archival HST data at the position of the potential optical counterpart DATE: 17/08/18 03:01:20 GMT FROM: Edo Berger at Harvard U R. J. Foley, C. D. Kilpatrick (UCSC), M. Nicholl, E. Berger (Harvard) report: The position of the potential optical counterpart (Coulter et al., LVC GCN 21529, Allam et al. LVC GCN 21530, Yang et al. LVC GCN 21531, Melandri et al. LVC GCN 21532) to the LIGO/Virgo G298048 trigger (LVC GCNs 21509, 21513) was imaged by the Hubble Space Telescope on 2017 April 28 UT with ACS in the F606W filter (Program ID: 14840; PI Bellini; 696 sec exposure time) as part of the "Schedule Gap Pilot Program." Examining the image we do not detect any sources within 2.2" of the nominal position to a 5-sigma limiting magnitude of ~25.9 mag, corresponding to M_V ~ -7.2 mag at a distance of 36 Mpc. We also note that the possible host galaxy, NGC 4993, has obvious dust lanes near its nucleus and extending out ~5" from the nucleus (corresponding to ~1 kpc at 36 Mpc). ------------------------------------------------- Edo Berger Professor of Astronomy Harvard University 60 Garden St. MS-19 Cambridge, MA 02138 USA Ph. 617-495-7914 / F. 617-258-7467 http://www.cfa.harvard.edu/~eberger ------------------------------------------------- //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21537 SUBJECT: LIGO/Virgo G298048: ATCA observations of candidate host galaxies DATE: 17/08/18 04:04:00 GMT FROM: Tara Murphy at U of Sydney K. Bannister (CSIRO), C. Lynch (University of Sydney), D. Kaplan (UWM), T. Murphy (University of Sydney), D. Dobie (University of Sydney) on behalf of the VAST collaboration. We are currently observing candidate host galaxies in the LIGO/Virgo G298048 localisation volume with the Australia Telescope Compact Array (LVC GCN #21513, sky map; LVC GCN #21519, 54 nearby galaxies). We are observing at two central frequencies of 8.5 GHz and 10.5 GHz, each with a bandwidth of 2 GHz. Observations started at 2017-08-18 01:00 UTC. Analysis of this data is underway. Subsequent epochs are planned. Thank you to CSIRO staff for supporting these observations. -- A/PROF TARA MURPHY | ARC Future Fellow Sydney Institute for Astronomy | School of Physics | Faculty of Science THE UNIVERSITY OF SYDNEY Room 358, Physics Building A28 The University of Sydney | NSW | 2006 T +61 2 9351 3041 E tara@physics.usyd.edu.au http://www.physics.usyd.edu.au/~tara https://www.coursera.org/learn/data-driven-astronomy //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21538 SUBJECT: LIGO/Virgo G298048: Las Cumbres Observatory Detection of The Possible Optical Counterpart in NGC 4993 DATE: 17/08/18 04:06:31 GMT FROM: Iair Arcavi at LCOGT I. Arcavi, D. A. Howell, C. McCully, G. Hosseinzadeh, S. Vasylyev (UCSB/Las Cumbres Obs), M. Zalzman, D. Poznanski (TAU), L.P. Singer (NASA/GSFC), S. Valenti (UC Davis), T. Piran (HUJI), D. Kasen, J. Barnes (UC Berkeley) and W-f. Fong (UA) report an independent detection of the possible optical counterpart reported by Coulter et al. (LVC GCN 21529), Chornock et al. (LVC GCN 21530), Valenti et al. (LVC GCN 21531) and Melandri et al. (LVC GCN 21532). In the course of Las Cumbres Observatory galaxy-targeted LIGO followup we observed NGC 4993 from one of our 1-meter telescopes at the Cerro Tololo Inter-American Observatory in Chile. An imaging 5-minute exposure starting at 2017-08-18 00:15:23 UT in the w (=g+r+i) filter clearly shows the candidate. Analysis of the image is ongoing and followup is planned when the field becomes visible to our Siding Spring telescopes starting at 2017-08-18 08:32 UT. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21539 SUBJECT: LIGO/Virgo G298048: DLT40 follow-up observation DATE: 17/08/18 04:11:35 GMT FROM: Sheng Yang at UC Davis Sheng Yang (INAF-OAPd, UC Davis), Stefano Valenti(UC Davis), David Sand (UA), Leonardo Tartaglia (UA, UC Davis), Enrico Cappellaro(INAF-OAPd), Dan Reichart, Josh Haislip (UNC) report on behalf of the Gravitational Wave Follow-Up by DLT40. We report the observation of 20 galaxies within the LVC error region for the GW trigger G298048 using the LIGO bayestar HLV localization map. We selected galaxies from the GWGC catalogue within 99.0% of the trigger error region, within a distance of 40.0 Mpc, brighter than -17.5 mag and at a Declination < 20 degree. Those selected galaxies have been observed using the Prompt 5 telescope and they are part of the ongoing DLT40 search. The DLT40 search limit magnitude, for those galaxies is 19.2 (open filter scaled to r band). Below follow the list of galaxies observed: Name RA(J2000) DEC(J2000) Dist(Mpc) BMAG KMAG NGC4594 189.9976 -11.623 9.77 -21.43 -24.9875 NGC5078 199.9585 -27.41 27.67 -21.24 -25.087 NGC5061 199.5213 -26.8371 24.21 -20.82 -24.631 NGC5101 200.4424 -27.4304 24.21 -20.68 -24.764 IC4197 197.0178 -23.7969 34.1 -20.24 -23.3868 NGC4993 197.4487 -23.3839 33.81 -20.2 -23.4212 NGC5188 202.8678 -34.7944 28.84 -20.2 -23.782 ESO508-024 197.6914 -23.8656 33.42 -19.98 -21.591 IC4180 196.7353 -23.917 33.65 -19.98 -23.0379 NGC5161 202.308 -33.1738 18.53 -19.84 -22.7064 NGC4968 196.7742 -23.6769 33.42 -19.44 -23.139 ESO508-019 197.4655 -24.2394 38.55 -19.33 -21.1601 IC0874 199.7521 -27.6287 29.06 -19.29 -22.6395 ESO508-003 196.6 -24.1641 33.43 -19.2 -21.2257 ESO576-001 197.599 -21.6841 35.47 -19.18 -21.9983 NGC4680 191.7282 -11.6367 29.92 -19.12 -22.6058 ESO576-003 197.6485 -21.7482 28.44 -18.94 -20.6476 ESO508-015 197.3286 -24.3846 33.42 -18.77 -18.785 NGC5042 198.8794 -23.9835 12.65 -18.7 -21.1145 ESO575-053 196.2705 -22.3839 30.48 -18.44 -21.3091 //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21541 SUBJECT: LIGO/VIRGO G298048: The Potential Optical Counterpart in NGC 4993 Has Afterglow-Like Colors DATE: 17/08/18 04:44:32 GMT FROM: Philip Cowperthwaite at Harvard U M. Nicholl (Harvard), P. S. Cowperthwaite (Harvard), S. Allam (Fermilab), J. Annis (Fermilab), E. Berger (Harvard), D. J. Brout (UPenn), D. Brown (Syracuse), R. E. Butler (Fermilab), H.-Y. Chen (Harvard), R. Chornock (Ohio University), E. Cook (TAMU), , H. T. Diehl (Fermilab), A. Drlica-Wagner (Fermilab), M. R. Drout (Carnegie), R. J. Foley (UCSC), W. Fong (Northwestern), D. Fox (Penn State), J. Frieman (Fermilab/UChicago), M.S.S. Gill (Stanford), R. Gruendl (NCSA), K. Herner (Fermilab), D. Holz (UChicago), R. Kessler (UChicago), R. Margutti (Northwestern), J. Marshall (TAMU), E. Neilsen (Fermilab), F. Paz-Chincon (NCSA), A. Rest (STScI), M. Sako (UPenn), N. Smith (Arizona), M. Soares-Santos (BrandeisU), D. Tucker (Fermilab), V. A. Villar (Harvard), A. Walker (NOAO), P. K. G. Williams (Harvard), B. Yanny (Fermilab), P. Lopes (UFRJ), F. Durret (IAP), A. Lourenço (UFRJ) On behalf of the DESGW+community team: We report preliminary optical i- and z-band photometry from DECam imaging of the possible optical counterpart to G298048 first identified in Coulter et al. (LVC GCN 21529), and further reported on by Allam et al. (LVC GCN 21530), Valenti et al. (LVC GCN 21531), Melandri et al. (LVC GCN 21532) and Arcavi et al. (GCN 21538). Observations were obtained on 2017-08-18 at 00:04 UTC. We find preliminary PSF magnitudes of i = 17.5 +/- 0.1 mag z = 17.5 +/- 0.1 mag This suggests an i-z color of 0 mag, which is consistent with the expected colors of a Short GRB afterglow, but not for lanthanide dominated kilonova emission (e.g., Barnes & Kasen 2013, Barnes et al. 2016, Wollaeger et al. 2017). These magnitudes are determined from difference PSF photometry of DECam images relative to Pan-STARRs 3pi catalogs. Further analysis is ongoing. [GCN OPC NOTE(18aug17): Per author's request, the trigger number in the Subject-line was changed from 298045 to 298048.] //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21542 SUBJECT: LIGO/Virgo G298048: Optical Candidate Shows No Evidence for Previous Activity in Archival SkyMapper Transient Survey Data DATE: 17/08/18 04:46:27 GMT FROM: Anais Moller at Australian National U A. Möller, S. Chang, C. Wolf We investigate SkyMapper Transient Survey data at the position of the optical source reported by Coulter et al. (LVC GCN 21529), Allam et al. (LVC GCN 21530), Yang et al. (LVC GCN 21531), Melandri et al. (LVC GCN 21532). We obtained subtraction photometry for the coordinates RA = 13:09:48.09 DECL. = -23:22:53.35 finding no evidence of variability between 2015-05-08 and 2017-07-22. The last observations of the SkyMapper Transient Survey of this field was on 2017-07-22 (limiting magnitude 19.6 in i) and 2017-07-21 (limiting magnitude 20.5 magnitude in r, 19.16 in i). The data and thumbnails can be found here: https://www.mso.anu.edu.au/skymapper/smt/extra The photometry is generated by placing an aperture at the indicated coordinates in difference images. Further observations are ongoing. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21543 SUBJECT: LIGO/Virgo G298048: Galaxy-Targeted Optical Followup With Las Cumbres Observatory DATE: 17/08/18 04:54:23 GMT FROM: Iair Arcavi at LCOGT I. Arcavi, D. A. Howell, C. McCully, G. Hosseinzadeh, S. Vasylyev (UCSB/Las Cumbres Obs), M. Zalzman, D. Poznanski (TAU), L.P. Singer (NASA/GSFC), S. Valenti (UC Davis), T. Piran (HUJI), D. Kasen, J. Barnes (UC Berkeley) and W-f. Fong (UA) report on optical followup observations of the LIGO-Virgo G298048 trigger using the Las Cumbres Observatory (LCO) worldwide telescope network. We target galaxies from the GLADE catalog and prioritize them by their position in the LIGO/Virgo localization region, their mass (estimated from their absolute B-band magnitude), and inversely by their distance. Between 2017-08-17 17:04 and 18:42 UT we observed the following galaxies using the two LCO 1-meter telescopes at the South African Astronomical Observatory in the following filters with a 300s exposure per filter: GLADE ID RA Dec Dist [Mpc] Galaxy B-mag Filters Observed 2037 199.749649 -47.908653 40.926 11.8 g,r,i 564852 214.019012 -48.127373 54.444 11.69 g,r 621160 194.532623 -46.264214 29.3765 10.93 g,r,i 732352 204.16272 -33.965916 49.125 11.24 g,r,i 737707 213.977814 -48.114883 59.917 12.06 g,r,i 815140 193.363815 -48.749153 49.556 11.98 g,r,i 1306036 198.491943 -49.478775 45.278 11.47 g,r,i 1850978 194.305 -46.37728 46.9894 12.12 g,r,i All r-band images were visually inspected for new sources compared to archival DSS images. No obvious ones were found. The above galaxies were chosen to also lie close to the FERMI localization region. Following the revised LIGO/Virgo localization from Singer et al. (LVC GCN 21513), we observed the following galaxies using the two LCO 1-meter telescopes at the Cerro Tololo Inter-American Observatory in Chile in the following filters with a 300s exposure per filter: GLADE ID RA Dec Dist [Mpc] Galaxy B-mag Filters Observed 341075 197.018005 -23.796844 34.097 12.87 w 564852 214.019012 -48.127373 54.444 11.69 g,r,i 602087 196.774902 -23.67704 33.42 13.18 w 645472 196.907242 -23.57892 41.75 14.21 w 667146* 197.448776 -23.383831 33.806 12.87 w 770765 196.89064 -24.008606 43.944 12.68 w 773496 196.735474 -23.91707 33.653 13.07 w 777014 196.270554 -22.383947 30.479 13.98 w 1366038 197.691406 -23.865728 33.42 12.64 w 1478047 197.466 -24.23937 38.548 13.6 w 1486718 196.937 -22.85784 26.792 12.88 w 1486724 197.329 -24.38456 33.42 13.85 w 1850989 197.465 -24.24 42.2669 12.78 w * GLADE 667146 is also NGC 4993 where we detect SSS17a / DLT17ck, the possible optical counterpart reported by Coulter et al. (LVC GCN 21529), Allam et al. (LVC GCN 21530), Yang et al. (LVC GCN 21531) and Melandri et al. (LVC GCN 21532). See Arcavi et al. (LCV GCN 21538). The w-band is wide filter covering the g+r+i-bands. Analysis of all images obtained is ongoing. The following GLADE galaxies have been submitted for observations starting at 2017-08-18 08:32 UT using the two LCO 1-meter telescopes at the Siding Spring Observatory in Australia with 300s w-band exposures: GLADE ID RA Dec Dist [Mpc] Galaxy B-mag 7 192.519547 -14.73349 53.528 13.21 626 193.998657 -19.26899 41.944 13.27 3644 192.248566 -14.399235 49.583 12.55 420937 198.880432 -23.982388 35.3367 12.31675 557076 194.366257 -19.691298 44.75 12.68 635635 196.600052 -24.164007 33.431 13.78 645300 196.580811 -22.98033 39.361 15.71 646603 193.219254 -15.413292 56.139 13.09 684330 193.363464 -17.005495 54.417 12.76 708169 196.666443 -22.455793 42.222 15.15 795473 199.096786 -26.561554 44.319 13.95 977319 194.252274 -17.320408 54.444 13.97 1486596 193.107 -15.51722 50.431 14.25 1486614 193.706 -16.0522 46.375 14.95 1486713 196.719 -22.84175 33.958 14.67 A spectrum of SSS17a / DLT17ck has also been submitted to start at 2017-08-18 08:32 UT using the LCO 2-meter telescope at Siding Spring, as well as g,r,i 300s imaging with one of the LCO 1-meter telescopes there. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21544 SUBJECT: LIGO/Virgo G298048: VISTA/VIRCAM detection of candidate counterpart DATE: 17/08/18 05:03:48 GMT FROM: Nial Tanvir at U of Leicester N. R. Tanvir (U. Leicester), A. J. Levan (U. Warwick) report on behalf of the VINROUGE collaboration. We observed the region around the location of the proposed optical counterpart of LIGO/Virgo G298048 (Coulter et al. LVC GCN 21529) using the VIRCAM camera on the wide-field ESO VISTA telescope. The source is clearly detected with a provisional magnitude J(AB)=17.5+/-0.1 at Aug-18 00:10 UT. We note that this is consistent with colours that are flat in Fnu, as noted by Nicholl et al. (LVC GCN 21541) from DECam data taken at a similar epoch. Further analysis is ongoing. We thank the staff at Paranal for their excellent support of these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21545 SUBJECT: LIGO/Virgo G298048: VLA Detection DATE: 17/08/18 05:07:58 GMT FROM: Kate Alexander at Harvard U K.D. Alexander, W. Fong, and E. Berger report on behalf of a larger collaboration: We observed the position of the optical candidate reported by Coulter et al. (LVC GCN 21529) and others (Allam et al. LVC GCN 21530, Valenti et al. LVC GCN 21531, Melandri et al. LVC GCN 21532, and Arcavi et al. GCN 21538) with the Very Large Array beginning at 2017 August 18 02:09:00 UT (13.5 h after the Fermi trigger time). At a mean frequency of 9.77 GHz, we detect a source with a preliminary flux density of ~0.3 mJy at the position: RA (J2000) =13:09:47.850 dec (J2000) =-23:23:01.29 with an error of 1.3" in each coordinate. This is consistent with the optical position reported by Coulter et al. Further observations are planned. We thank the VLA staff for rapidly executing these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21546 SUBJECT: LIGO/Virgo G298048: MASTER observations of the NGC 4993 DATE: 17/08/18 05:37:59 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs V.M. Lipunov, E. Gorbovskoy, V.G.Kornilov, N.Tyurina, V.Shumkov, D.Kuvshinov, P.Balanutsa, O.Gress, A.Kuznetsov, M.I.Panchenko, A.V.Krylov, I.Gorbunov Lomonosov Moscow State University, Sternberg Astronomical Institute R.Podesta, C.Lopez, F. Podesta Observatorio Astronomico Felix Aguilar (OAFA) , National University of San Juan, Argentina H. Levato, C. Saffe Instituto de Ciencias Astronomicas,de la Tierra y del Espacio (ICATE), San Juan, Argentina N.M. Budnev, O. Gress, K. Ivanov, S.Yazev Irkutsk State University V.Yurkov, Yu.Sergienko, A.Gabovich Blagoveschensk Educational State University, Blagoveschensk D.Buckley, S. Potter, M. Kotze, South African Astronomical Observatory R. Rebolo, M. Serra-Ricart, G. Israelian, N.Lodiu The Instituto de Astrofisica de Canarias A. Tlatov, V.Sennik Kislovodsk Solar Station of the Pulkovo Observatory MASTER-OAFA have imaged the BAYESTAR localization map of LIGO/Virgo G298048 (GCN 21513). We have images of NGC 4993 galaxy starting 2017-08-17 23:59:54UT with 19.5 limit. We see object detected by S. Allam et al., (GCN 21530). This message can be citted. [GCN OPS NOTE(18aug17): Per author's request, the ID number in the Subject-line was changed from G297595 to G298048.] //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21547 SUBJECT: LIGO/VIRGO G298048: Magellan Optical Spectrum of the Potential Optical Counterpart Associated with NGC 4993 DATE: 17/08/18 05:46:33 GMT FROM: Ryan Foley at UCSC M. R. Drout, J. D. Simon, B. J. Shappee (Carnegie), K. Boutsia, J. Bravo, G. Prieto (Las Campanas Observatory), D. A. Coulter, R. J. Foley, C. D. Kilpatrick, M. R. Siebert (UCSC), and A. L. Piro (Carnegie) report On 2017 Aug 18.02 UT, we obtained an optical spectrum of the transient source SSS17a (RA = 13:09:48.09 DECL. = -23:22:53.35, Coulter et al. 2017; GCN 21529) possibly associated with LIGO/Virgo G298048, with the LDSS-3 spectrograph on the 6.5m Magellan-Clay telescope at Las Campanas Observatory. The resulting spectrum shows a blue and featureless continuum between 4000 and 10,000 Angstroms, consistent with a power-law. Additional observations are encouraged. [GCN OPS NOTE(18aug17): Per author's request, the trigger ID in the Subject-line was corected from 298045 to 298048.] //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21548 SUBJECT: LIGO/Virgo G298048: VLA Refined Analysis DATE: 17/08/18 06:56:44 GMT FROM: Kate Alexander at Harvard U K.D. Alexander (Harvard), W. Fong (Northwestern), and E. Berger (Harvard) report on behalf of a larger collaboration: We have completed a more thorough analysis of the VLA observations previously reported by Alexander et al. (LVC GCN 21529), in which we detected radio emission near the position of the candidate optical counterpart to LIGO/Virgo G298048. We now believe that the previously reported position underestimated the coordinate uncertainties created by the highly elongated beam shape (~9" by 1.5") due to the low elevation of the target. We note that the center of the observed VLA position is actually closer to the position of the candidate host galaxy, NGC 4993, than to the position of the optical transient reported by Coulter et al. (LVC GCN 21529), and may contain an unknown amount of host contribution. At this time we cannot state with confidence whether this radio emission originates from the galaxy or the optical transient. Analysis is ongoing and further observations are planned. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21549 SUBJECT: LIGO/Virgo G298048: Subaru HSC follow-up observations DATE: 17/08/18 07:07:07 GMT FROM: Yousuke Utsumi at Hiroshima Astrophys. Science Center Yoshida, M., Tanaka, M., Terai, T., Nakata, F., Furusawa, H., Koshida, S. (NAOJ), Utsumi, Y., Kawabata K. S. (Hiroshima Univ.), Tominaga, N. (Konan Univ.), Motohara, K., Ohsawa, R., Morokuma, T. (Univ. of Tokyo), Kawai, N. (Tokyo Tech) on behalf of the J-GEM collaboration We performed follow-up observations for the gravitational event G298048 (GCN 21505; 21509; 21513) with Hyper Suprime-Cam attached to the Subaru telescope on August 18 2017 UT. The observations started at 5:20 UT and were continued until 6:00 UT. We used HSC-z band filter. The sky area of about 25 deg2 centered at (alpha, delta) = (-162.8 deg, -25 deg) was covered with 24 HSC pointings. This area includes the candidate of optical counterpart (SSS17a) in the galaxy NGC 4993 reported by Coulter et al. (GCN 21529) and covers 60% of the probability area of the LALInference skymap (GCN 21527). Typical exposure time was 30 seconds. SSS17a is clearly seen in our z-band images. We made rough photometry of this object and obtained z-band magnitude of ~17 (AB). Further analysis is on going. The sky fields and galaxies observed by this survey are listed below: ID Time RA DEC Exp Filter ----------------------------------------------------------- 28 2017-08-18T05:08:43 13h10m22.9s -23d18m49.1s 2.0s HSC-z 28 2017-08-18T05:12:13 13h10m22.9s -23d18m49.0s 2.0s HSC-z 28 2017-08-18T05:15:23 13h10m22.9s -23d18m49.1s 2.0s HSC-z 28 2017-08-18T05:16:25 13h10m22.9s -23d18m49.0s 2.0s HSC-z 28 2017-08-18T05:20:04 13h10m22.9s -23d18m49.0s 2.0s HSC-z 04 2017-08-18T05:21:18 13h07m34.2s -26d36m20.9s 5.0s HSC-z 28 2017-08-18T05:22:43 13h10m14.4s -23d19m20.0s 1.2s HSC-z 28 2017-08-18T05:25:56 13h10m14.5s -23d19m20.2s 1.2s HSC-z 28 2017-08-18T05:30:27 13h10m14.4s -23d19m20.1s 20.0s HSC-z 05 2017-08-18T05:32:00 13h10m23.0s -27d16m31.1s 30.0s HSC-z 06 2017-08-18T05:33:00 13h13m11.8s -27d56m56.0s 30.0s HSC-z 07 2017-08-18T05:34:03 13h16m00.6s -28d37m36.1s 30.0s HSC-z 08 2017-08-18T05:35:03 13h18m49.3s -29d18m32.0s 30.0s HSC-z 09 2017-08-18T05:36:03 13h21m38.1s -29d59m44.5s 30.0s HSC-z 10 2017-08-18T05:37:09 13h04m45.4s -24d37m11.8s 30.0s HSC-z 11 2017-08-18T05:38:10 13h07m34.2s -25d16m41.8s 30.0s HSC-z 12 2017-08-18T05:39:10 13h10m22.9s -25d56m24.5s 30.0s HSC-z 28 2017-08-18T05:40:10 13h10m22.9s -23d18m48.9s 60.0s HSC-z 13 2017-08-18T05:41:41 13h13m11.7s -26d36m21.0s 30.0s HSC-z 14 2017-08-18T05:42:42 13h01m56.6s -22d39m54.9s 30.0s HSC-z 15 2017-08-18T05:43:45 13h16m00.5s -27d16m31.1s 30.0s HSC-z 16 2017-08-18T05:44:46 13h18m49.3s -27d56m55.9s 30.0s HSC-z 17 2017-08-18T05:45:50 13h04m45.4s -23d18m48.9s 30.0s HSC-z 18 2017-08-18T05:46:51 13h07m34.1s -23d57m54.5s 30.0s HSC-z 19 2017-08-18T05:47:52 12h59m07.8s -20d44m16.9s 30.0s HSC-z 20 2017-08-18T05:48:54 13h10m22.9s -24d37m12.1s 30.0s HSC-z 22 2017-08-18T05:49:55 13h13m11.7s -25d16m41.9s 30.0s HSC-z 23 2017-08-18T05:50:55 13h16m00.4s -25d56m24.5s 30.0s HSC-z 24 2017-08-18T05:52:05 12h56m19.0s -18d50m06.2s 30.0s HSC-z 25 2017-08-18T05:53:09 13h04m45.3s -22d01m12.0s 30.0s HSC-z 26 2017-08-18T05:54:11 13h07m34.1s -22d39m55.1s 30.0s HSC-z 29 2017-08-18T05:55:16 13h01m56.5s -20d06m04.1s 30.0s HSC-z ----------------------------------------------------------- # observed galaxy list Name RA DEC -------------------------------- GL125437-181830 193.6546 -18.3082 GL125600-191608 193.9987 -19.269 GL125703-193105 194.261 -19.5181 GL125812-210245 194.55 -21.046 GL130407-250220 196.031 -25.0388 GL130415-225252 196.063 -22.8812 GL130505-222302 196.2706 -22.3839 GL130524-233121 196.348 -23.5226 GL130525-233009 196.354 -23.5025 GL130619-225849 196.5808 -22.9803 GL130624-240950 196.6001 -24.164 GL130640-222721 196.6664 -22.4558 GL130653-225030 196.719 -22.8418 GL130657-235501 196.7355 -23.9171 GL130706-234037 196.7749 -23.677 GL130708-240641 196.782 -24.1114 GL130731-231014 196.879 -23.1705 GL130734-234855 196.892 -23.8152 GL130734-240031 196.8906 -24.0086 GL130738-233444 196.9072 -23.5789 GL130738-235618 196.907 -23.9384 GL130745-225128 196.937 -22.8578 GL130804-234749 197.018 -23.7968 GL130832-232050 197.135 -23.3472 GL130842-234633 197.177 -23.7757 GL130842-242258 197.175 -24.3828 GL130918-242255 197.324 -24.3821 GL130919-242304 197.329 -24.3846 GL130948-232302 197.4488 -23.3838 GL130952-241422 197.466 -24.2394 GL130952-241424 197.465 -24.24 GL131000-234253 197.4993 -23.7146 GL131001-264243 197.504 -26.7118 GL131007-263543 197.529 -26.5953 GL131023-275837 197.595 -27.977 GL131046-235157 197.6914 -23.8657 GL131110-280037 197.79 -28.0103 GL131247-255912 198.195 -25.9866 GL131406-290116 198.5231 -29.0212 GL131418-263458 198.5739 -26.5827 GL131427-271243 198.611 -27.212 GL131531-281703 198.8771 -28.2841 GL131608-282438 199.0349 -28.4105 GL131610-291131 199.04 -29.192 GL131611-283941 199.0473 -28.6613 GL131616-292111 199.0658 -29.353 GL131618-292642 199.0742 -29.4449 GL131620-281709 199.0837 -28.2857 GL131623-263342 199.0968 -26.5616 GL131645-275310 199.189 -27.8861 GL131651-283105 199.2137 -28.5181 GL131657-252015 199.239 -25.3375 GL131748-265409 199.45 -26.9025 GL131752-264748 199.465 -26.7966 GL131805-265014 199.5211 -26.8372 GL131824-272606 199.6 -27.435 GL131901-273743 199.7522 -27.6285 GL131939-284424 199.9116 -28.7401 GL131941-272544 199.919 -27.429 GL131950-272436 199.9584 -27.4101 GL132014-300209 200.058 -30.036 GL132045-302028 200.188 -30.341 GL132050-292847 200.2091 -29.4798 GL132109-303927 200.2879 -30.6575 GL132208-304240 200.532 -30.7112 GL132218-300915 200.575 -30.1543 GL132324-293551 200.8513 -29.5976 GL132331-300651 200.8777 -30.1143 GL132343-300324 200.9291 -30.0568 GL132414-301522 201.06 -30.256 GL132425-301505 201.1048 -30.2514 GL132428-302555 201.1148 -30.4319 ---------------------------------- //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21550 SUBJECT: LIGO/VIRGO G298048: Swift UVOT detection and XRT upper limits DATE: 17/08/18 07:24:04 GMT FROM: Phil Evans at U of Leicester P.A. Evans (U. Leicester), J.A. Kennea (PSU), A.A. Breeveld (UCL-MSSL), S. Campana (INAF-OAB), S.B. Cenko (NASA/GSFC), E. Troja (NASA/GSFC/UMCP), P.T. O'Brien (U. Leicester), S.D. Barthelmy (NASA/GSFC), A.P. Beardmore (U. Leicester), D.N. Burrows (PSU), G. Cusumano (INAF-IASF PA), A. D'Ai (INAF-IASFPA), P. D'Avanzo (INAF-OAB), V.D'Elia(ASDC), S.W.K. Emery (UCL-MSSL), P. Giommi (ASI), C. Gronwall (PSU), H.A. Krimm (CRESST/GSFC/USRA), N.P.M. Kuin (UCL-MSSL), A.Y. Lien (GSFC/UMBC), F.E. Marshall (NASA/GSFC), A. Melandri (INAF-OAB), J.A. Nousek (PSU), S.R. Oates (U. Warwick), J.P. Osborne (U. Leicester), C. Pagani (U. Leicester), K.L. Page (U.Leicester), D.M. Palmer (LANL), M. Perri (ASDC), J.L. Racusin (NASA/GSFC), B. Sbarufatti (INAF-OAB/PSU), M.H. Siegel (PSU), G. Tagliaferri (INAF-OAB), A. Tohuvavohu (PSU) report on behalf of the Swift team: Swift has performed ToO observations of the proposed optical counterpart of LIGO/Virgo G298048 (Coulter et al. LVC GCN 21529). We obtained 2 ks of data from 53.8 to 55.8 ks after the LVC trigger. No X-ray source is detected at the location of the transient reported by Coulter et al. The 3-sigma upper limit at this location is 4.5e-3 ct/sec. For a typical GRB spectrum this corresponds to 1.8e-13 erg/cm^2/s (0.3-10 keV). Assuming a distance of 40 Mpc this corresponds to a 0.3-10 keV luminosity of 3.5e40 erg/s. D'Avanzo et al (2014, MNRAS, 442, 2342) compiled the observed 2-10 keV luminosity at 11 hours post-trigger for a complete sample of Swift-detected short GRBs; these were typically of order 1e41-1e43 erg/s. Our measurement corresponds to a 2-10 keV luminosity of 2.3e40 erg/s, ~an order of magnitude fainter than all of the other sGRBs in that paper apart from GRB 080905. However those authors also showed a correlation between Eiso and X-ray afterglow luminosity, so given the low Eiso (Goldstein et al., LVC Circ. 21528) this may not be surprising. The afterglow is detected in the Swift-UVOT data. Analysis is complicated by the nearby presence the galaxy NGC4993, but we obtain the following magnitudes: Filter Magnitude Start time Stop time u 16.9 0.06 T0+53.8 ks T0+54.5 ks w1 17.74 0.09 T0+55.0 ks T0+55.3 ks m2 19.26 0.18 T0+54.5 ks T0+55.0 ks w2 19.12 0.17 T0+55.3 ks T0+55.8 ks We note that it is very unusual for an optical counterpart to be found but no X-ray counterpart, especially given the brightness of the optical counterpart. Therefore, if this object is a GRB afterglow, it is atypical compared to the sample of Swift-BAT triggered objects observed to date. We suggest therefore that the object may be a blue (i.e. lanthanide-free) kilonova. This circular is an official product of the Swift team. [GCN OPS NOTE(18aug17): Per author's request, the trigger ID in the Subject-line was corected from 298045 to 298048.] //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21551 SUBJECT: LIGO/Virgo G298048: Magellan g-band Imaging of the Potential Optical Counterpart Associated with NGC 4993 DATE: 17/08/18 07:54:23 GMT FROM: Mansi M. Kasliwal at Caltech J. D. Simon, B. J. Shappee, M. R. Drout (Carnegie), D. A. Coulter, R. J. Foley, C. D. Kilpatrick, M. R. Siebert (UCSC), K. Boutsia, J. Bravo, G. Prieto (Las Campanas Observatory), and A. L. Piro (Carnegie) On 2017 Aug 18.01 UT we obtained g-band images of the transient source SSS17a (RA = 13:09:48.09 DECL. = -23:22:53.35, Coulter et al. 2017; GCN 21529) possibly associated with LIGO/Virgo G298048, with LDSS-3 on the 6.5m Magellan-Clay telescope at Las Campanas Observatory. We measure a provisional magnitude of g = 17.2 +/- 0.1, consistent with the blue color reported spectroscopically by Drout et al. 2017 (GCN 21547) and at redder wavelengths by Nicholl et al. 2017 (GCN 21541). We also note a tentative detection of a slight decrease in brightness over three exposures spanning 12 minutes. Further analysis is ongoing. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21552 SUBJECT: LIGO/Virgo G298048: Gemini-South Near-Infrared Photometry of the Optical Transient Candidate DATE: 17/08/18 08:00:58 GMT FROM: Leo Singer at NASA/GSFC L. P. Singer (NASA/GSFC), R. Lau (Caltech), M. M. Kasliwal (Caltech), D. Cook (Caltech), S. Bradley Cenko (NASA/GSFC), J. Cannizzo (NASA/GSFC), S. Nissanke (RU), and I. Arcavi (UCSB/Las Cumbres Obs) report on behalf of the Global Relay of Observatories Watching Transients Happen (GROWTH) collaboration: On 2017 Aug 18.06 UT, we obtained near-infrared observations with the FLAMINGOS-2 instrument on Gemini-South of the field of the optical transient candidate SSS17a (Coulter et al., GCN 21529; Allam et al., GCN 21530; Yang et al., GCN 21531, Melandri et al., GCN 21532; etc.) that was reported in connection with the LIGO/Virgo candidate G298048 (LVC, GCNs 21509, 21510, 21513). We obtained 230 s of imaging in K_s band. A source is clearly visible at a position that is consistent with the previously reported optical transient. Calibrating to the 2MASS Point Source Catalog, we measure a K_s-band magnitude of 16.9 +/- 0.2 (Vega). In addition to the optical transient, we also obtained K_s band imaging of two of the 13 galaxies in the Census of the Local Universe (CLU) cross-match with the BAYESTAR face-on localization (Cook et al., GCN 21521). We plan to observe the remaining galaxies over the coming nights. We thank Gemini Observatory for rapidly reviewing and awarding us directors' discretionary time under which these observations were taken. We thank H. Kim and K. Silva, and the rest of the Gemini-South staff, for promptly executing these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21553 SUBJECT: LIGO/Virgo G298048: Pan-STARRS detections and izy photometry of the possible optical/NIR counterpart in NGC4993 DATE: 17/08/18 08:37:20 GMT FROM: S. J. Smartt at Queens U Belfast K. C. Chambers (IfA), M. E. Huber (IfA), S. J. Smartt, (QUB), K. W. Smith (QUB), D. R. Young, M. Coughlin (Harvard), T.-W. Chen (MPE), L. Denneau, H. Flewelling, A. Heinze, E. Kankare (QUB), T. Lowe, E. A. Magnier (IfA), A. Rest (STScI), B. Stalder (IfA), A. S. B. Schultz, C. W. Stubbs (Harvard) J. Tonry, C. Waters, R. J. Wainscoat, H. Weiland, M. Willman (IfA), D. E. Wright (QUB) We report Pan-STARRS imaging observations of the the skymap of G298048. A set of six images were taken, in twilight and at low airmass. We had planned to tile the northern part of the skymap, but after the discovery of the transient SSS17a/DLT17ck in GCN 21529 (Coulter et al) and 21531 (Valenti et al.) we immediately switched to cover the NGC4993 in 2x30s in each of Pan-STARRS i, z, y, ensuring the postion of the transient object was on a good, clean CCD cell. Difference images were produced by subtracting the Pan-STARRS1 3Pi reference image from these separate 30s exposures (Chambers et al. arXiv:1612.05560, and available at http://panstarrs.stsci.edu). We recover the transient as Pan-STARRS object PS17gl at coordinates RA = 13:09:48.08 DEC = -23:22:53.2 RA = 197.45033 DEC = -23.38144 Image log and photometry in the Pan-STARRS system (Tonry et al. 2012 Magnier et al. arXiv:1612.05242) : Date (UT) RA DEC Exp Filt Airmass 2017-08-18T05:33:01 198.347081 -23.075627 2000 30.0 y 2.83 17.28 0.13 2017-08-18T05:33:46 198.347076 -23.075658 2000 30.0 z 2.84 17.31 0.09 2017-08-18T05:34:31 198.347062 -23.075632 2000 30.0 i 2.86 17.23 0.10 2017-08-18T05:35:45 198.347073 -23.075633 2000 30.0 y 2.89 17.47 0.16 2017-08-18T05:36:30 198.347070 -23.075638 2000 30.0 z 2.91 17.21 0.08 2017-08-18T05:37:14 198.347060 -23.075617 2000 30.0 i 2.93 17.26 0.08 There is no evidence, within the uncertainties for fading between the exposures. If the Swope 1m photometry point of i=16 (Coulter et al.) is correct then this would imply substantial fading. But this needs checked, since DLT17ck was reported at R=17.3, is more consistent with the colours we measure : i - z = -0.02 +/- 0.02 z - y = -0.26 +/- 0.18 This is consistent with the DECam photometry by Nicholl et al. (GCN21541) and that within the uncertainties, the colours are consistent with 0, and being flat in Fnu as reported by the J-band detection of Tanvir & Levan (GCN21544). Further observations are planned with the same filter setup as long as the target is observable, or firmly ruled out as a counterpart to G298048. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21554 SUBJECT: LIGO/Virgo G298048: HCT observations DATE: 17/08/18 09:54:21 GMT FROM: Varun Bhalerao at Indian Inst of Tech M. Pavana, B.S. Kiran, G.C. Anupama (IIA), Varun Bhalerao (IIT Bombay) on behalf of the GROWTH collaboration report: We observed four fields corresponding to IceCube neutrino events (Bartos et al., GCN 21508) with the 2 metre Himalayan Chandra Telescope (HCT). We used the HFOSC instrument with a 10' x 10' FoV to obtain 3 R band exposures of 180 seconds each for the following fields: RA (deg) Dec(deg) 291.4 69.0 226.7 12.0 291.3 68.8 01.4 23.8 Visual inspection of the images shows no new source that could be associated with G298048. We note that all four locations are outside the revised HLV localisation region (LIGO Scientific Collaboration et al, GCN 21513). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21555 SUBJECT: LIGO/Virgo G298048, Fermi GBM trigger 524666471/170817.529: MAXI/GSC observations DATE: 17/08/18 10:43:45 GMT FROM: Satoshi Sugita at Tokyo Inst. of Tech. S. Sugita, N. Kawai (Tokyo Tech), M. Serino (RIKEN), H. Negoro (Nihon U.), S. Ueno, H. Tomida, M. Ishikawa, Y. Sugawara, N.Isobe, R. Shimomukai (JAXA), T. Mihara, M. Sugizaki, S. Nakahira, W. Iwakiri, M. Shidatsu, M. Matsuoka (RIKEN), T. Yoshii, Y. Tachibana, S. Harita, Y. Muraki, K. Morita (Tokyo Tech), A. Yoshida, T. Sakamoto, Y. Kawakubo, Y. Kitaoka, T. Hashimoto (AGU), H. Tsunemi, T. Yoneyama (Osaka U.), M. Nakajima, T. Kawase, A. Sakamaki (Nihon U.), Y. Ueda, T. Hori, A. Tanimoto, S. Oda (Kyoto U.), Y. Tsuboi, Y. Nakamura, R. Sasaki (Chuo U.), M. Yamauchi, C. Hanyu, K, Hidaka (Miyazaki U.), T. Kawamuro (NAOJ), K. Yamaoka (Nagoya U.) report on behalf of the MAXI team: We examined the MAXI/GSC all-sky X-ray images (2-20 keV) obtained in the orbits following LIGO/Virgo trigger G298048 and the Fermi GBM trigger 524666471/170817.529 at 2017-08-17 12:41:06.47 UTC (GCN 21506). At the trigger time of Fermi GBM, the high-voltage of MAXI/GSC was off, and it was turned on at T0+173 sec. The center of the Fermi GBM localization was located near the pole of ISS orbital rotation, where the MAXI/GSC cannot cover the field. The field of candidate optical counterpart (GCN 21529) was marginally covered by MAXI and was scanned at 12:23 UT (18 min before the trigger), but the OT position was obscured by an ISS structure. The OT candidate position was difficult to cover with MAXI/GSC due to unfavorable orientation of the orbital plane of the ISS, and therefore it was not observed for the following 8 orbits. The first scan by MAXI/GSC was started at 08-18 02:19 UTC (818 min after the LIGO trigger). We did not detect a significant source at this position with a 3-sigma upper limit of 54 mCrab. This limit is higher than the typical value because of high particle background flux. For the remaining area of the G298048 preliminary-LALInference skymap, we obtained a typical 1(3)-sigma upper limit of 11(33) mCrab in the orbit following the trigger. If you require information of X-ray flux by MAXI/GSC at specific coordinates, please contact the submitter of this circular by email. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21556 SUBJECT: LIGO/Virgo G298048: REM optical/NIR observations DATE: 17/08/18 10:54:42 GMT FROM: Andrea Melandri at INAF-OAB A. Melandri, P. D'Avanzo, S. Campana, S. Covino (INAF-OAB), G. Greco (Urbino University/INFN Firenze), M. Branchesi (GSSI), D. Fugazza (INAF-OAB), L. Amati (INAF-IASF Bo), L. A. Antonelli, (INAF-OAR), S. Ascenzi (INAF-OAR), M.T. Botticella (INAF-OAC), E. Cappellaro (INAF-OAPD), V. D'Elia (INAF-ASDC), F. Getman (INAF-OAC), A. Grado (INAF-OAC), L. Limatola (INAF-OAC), M. Lisi (INAF-OAR), L. Nicastro (INAF-IASF Bo), E. Palazzi (INAF-IAFS Bo), E. Pian (SNS-Pisa), S. Piranomonte (INAF-OAR), L. Pulone (INAF-OAR), A. Rossi (INAF-IASF Bo), G. Stratta (Urbino University/INFN Firenze), G. Tagliaferri (INAF-OAB), V. Testa (INAF-OAR), L . Tomasella (INAF-OAPD), S. Yang (INAF-OAPD), E. Brocato (INAF-OAR) on behalf of GRavitational Wave Inaf TeAm report: We carried out optical/NIR follow-up observations of the LIGO/Virgo GW trigger G298048 (LVC GCN Circ. 21509, 21513) with the 60-cm robotic telescope REM located at the La Silla Observatory (Chile) by performing targeted observations of catalogued galaxies in the LVC skymap. The observations were carried out from 23:11:29 UT on 2017 Aug 17 (i.e. 10.5 hours after the event detection) to 02:08:24 UT on on 2017 Aug 18, simultaneously in the g, r, i, z and H bands. We observed 18 galaxies (see table below). Group1 targets were selected within 3sigma from the position of the neutrino candidate reported in LVC GCN Circ. 21511, with a distance consistent with the GW trigger; Group2 targets are a sub-sample of the galaxies within the 50% probability region reported in the LVC GCN Circ. 21516; Group3 targets are galaxies reported in LVC GCN Circ. 21519, 21521. RA(J2000) Dec(J2000) Distance (Mpc) ---Group1 12:04:20.16 -01:31:49.58 27.41 12:01:11.04 -01:17:43.30 28.19 12:13:38.88 -01:17:36.56 34.27 12:02:31.68 -02:18:11.52 40.08 12:16:44.16 -02:48:37.08 45.95 12:06:52.80 -04:02:36.96 26.25 12:00:24.96 -04:54:49.32 35.73 * --------------------------------------- ---Group2 12:57:27.90 -19:41:28.67 44.75 13:07:33.75 -24:00:30.98 43.94 13:08:04.32 -23:47:48.64 34.09 13:06:56.51 -23:55:01.45 33.65 13:07:05.97 -23:40:37.34 33.42 13:07:37.73 -23:34:44.11 41.75 13:06:24.01 -24:09:50.42 33.43 13:07:37.68 -23:56:18.11 45.98 13:06:19.39 -22:58:49.18 39.36 --------------------------------------- ---Group3 13:09:47.68 -23:23:02.03 41.66 13:16:23.25 -26:33:41.03 45.59 *: we detected a possible optical source in this field at the following coordinates: RA(J2000),Dec(J2000) = 12:00:26.76,-04:55:04.2 (+/- 0.5"). This source is faint, having a magnitude of r~19.3 (i.e. close to the limiting magnitude of our observations) and we cannot establish the nature of this objects. However, its position seems to be consistent (within 3 arcmin) with a minor planet (23444-Kukucin). A preliminary analysis (also based on visual comparison with the DSS) reveals no obvious optical/NIR candidate counterpart in the above galaxies down to the following magnitudes: r > 19.5, H > 17.0 (AB, 3sigma UL). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21557 SUBJECT: LIGO/Virgo G298048: Likelihood of SSS17a Being an Unrelated Extragalactic Transient in NGC 4993 DATE: 17/08/18 12:15:23 GMT FROM: Ryan Foley at UCSC R. J. Foley (UC Santa Cruz) reports In the interest of focusing follow-up observing resources, we perform a quick assessment of how “unique” the potential EM counterpart to the LIGO/Virgo G298048 trigger (LVC GCNs 21509, 21513), SSS17a (Coulter et al., LVC GCN 21529), is in the context of other extragalactic astrophysical transients. The optical spectrum (Drout et al., LVC GCN 21547) and colors (Nicholl et al., LVC GCN 21541; Chambers et al., LVC GCN 21553) are inconsistent with a Type Ia supernova at any epoch. Its nominal host galaxy, NGC 4993, is an S0 galaxy, which typically have little star formation (although there are dust lanes near the SN position; Foley et al., LVC GCN 21536). If at the distance of its nominal host galaxy, NGC 4993, correcting for only Milky Way extinction, SSS17a had a peak luminosity of M_g ~ -16.0 mag (e.g., Simon et al., LVC GCN 21551), which is much more luminous than novae, much less luminous than SNe Ia near peak, and similar to some core-collapse SNe near peak. The lack of a strong source in recent imaging (Cowperthwaite et al., LVC GCN 21533) indicates that SSS17a is <~ 2 days old. At the very least, there was no source to deep limits from Hubble images ~4 months ago (Foley et al., LVC GCN 21536). These data provide strongly constraining information on the nature of SSS17a. Approximately 7.3% of all supernovae in S0 galaxies are core-collapse galaxies (Foley & Mandell, 2013, ApJ, 778, 167). Using the luminosity of NGC 4993 and the formulae of Li et al. (2011, MNRAS, 412, 1473), we find that ~17% of all supernovae in S0 galaxies with a similar luminosity to that of NGC 4993 are core-collapse SNe. Using the Li et al. local volumetric core-collapse rate, we expect ~0.1 core-collapse SN per year in the 90% LIGO localization volume. A core-collapse SN exploding within 2 days of the LIGO trigger and within this volume has a probability of roughly 5 x 10^-5. Including all SNe, this number only increases to 8 x 10^-5. The probability of a core-collapse SN exploding since the Hubble images were obtained inside the LIGO volume is ~0.003. We note that these calculations do not account for possible overdensities, and NGC 4993 is a member of a relatively massive group of galaxies. Finally, examining the core-collapse luminosity functions of Li et al. (2011, MNRAS, 412, 1441), ~50% of Type Ib/c supernovae and ~65% of Type II supernovae in S0-Sbc galaxies have peak absolute magnitudes greater than -16.0 mag. That is, roughly half of all core-collapse SNe in S0-Sbc galaxies never reach the reported magnitude of SSS17a. Combined, we estimate that the likelihood of SSS17a being an unrelated core-collapse SN in NGC 4993 to be ~5 x 10^-6. Excluding the strongest constraints related to possible recent non-detections, the likelihood of SSS17a being an unrelated core-collapse SN in NGC 4993 is ~3 x 10^-4. We conclude that SSS17a is a rare event, and warrants significant additional follow-up observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21558 SUBJECT: LIGO/Virgo G298048: TZAC TAROT Reunion (TRE) observations DATE: 17/08/18 13:04:25 GMT FROM: Michel Boer at CESR-CNRS A. Klotz (IRAP CNRS/UPS), R. Laugier, M. Boer, K. Noysena (ARTEMIS CNRS/UCA/OCA) report on behalf of the TZAC collaboration We have observed the initial error box with the TRE (TAROT-Reunion) Telescope located at Les Makes Observatory, La Réunion Island, France. Each image (no filter) lasts for 120s and covers a field of 4.2 x 4.2 deg2, with a magnitude limit of 17.0. Unfortunately the position of the candidate afterglow reported by Coulter et al. (LVC GCN 21529) was not in the position observable at that time given the automated generation of the fields, the mixed weather conditions, and the position of the GW candidate transient in the sky. We list below the log of the observations. Images are under analysis. Date RA DEC 2017-08-17T17:48:54 220.121 -43.833 2017-08-17T17:51:01 220.119 -43.832 2017-08-17T18:20:39 228.450 -48.036 2017-08-17T18:22:46 228.448 -48.035 2017-08-17T18:25:02 219.216 -52.230 2017-08-17T18:27:09 219.213 -52.228 2017-08-17T18:29:16 219.212 -52.226 2017-08-17T22:06:59 32.142 +40.179 2017-08-17T22:09:06 31.598 +40.180 2017-08-17T22:11:14 31.087 +40.183 2017-08-17T22:36:21 34.642 +42.385 2017-08-17T22:38:28 36.473 +40.141 2017-08-18T00:29:44 41.936 +40.144 2017-08-18T00:31:50 41.938 +40.143 2017-08-18T01:18:34 41.901 +40.145 2017-08-18T01:20:41 41.903 +40.145 2017-08-18T00:33:59 30.905 +40.147 2017-08-18T00:36:06 30.907 +40.147 2017-08-18T00:38:14 30.909 +40.147 2017-08-18T01:22:57 30.870 +40.151 2017-08-18T01:25:04 30.872 +40.151 2017-08-18T01:27:11 30.874 +40.151 2017-08-18T01:05:32 36.396 +40.145 2017-08-18T01:07:39 36.398 +40.145 2017-08-18T01:52:20 36.369 +40.149 2017-08-18T01:54:27 36.371 +40.150 2017-08-18T01:56:34 36.373 +40.151 //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21559 SUBJECT: LIGO/Virgo G298048: ATCA detection of a radio source coincident with NGC 4993 DATE: 17/08/18 13:27:25 GMT FROM: Keith Bannister at ATNF K. Bannister (CSIRO), C. Lynch (University of Sydney), D. Kaplan (UWM), T. Murphy (University of Sydney), D. Dobie (University of Sydney) on behalf of the VAST collaboration. We observed 54 candidate host galaxies in the LIGO/Virgo G298048 localisation volume with the Australia Telescope Compact Array (LVC GCN 21513, sky map; LVC GCN 21519, 54 nearby galaxies). Observations started at 2017-08-18 01:00 UT and ended at 2017-08-18 09:14:15 UT with approximately 1-2 minutes of on-source time for each target. We detect an unresolved radio source coincident with NGC 4993. The best-measured position was at 8.5 GHz: RA = 13:09:47.7 Dec = -23:22:59.1 (J2000) with positional errors of 1” in RA and 4” in declination. This position is in agreement with the VLA detection of a radio source (Alexander et al. LVC GCN 21548) within the stated errors of each observation. We report preliminary flux densities of: ~0.6 mJy at 8.5 GHz ~0.5 mJy at 10.5 GHz ~0.4 mJy at 16.7 GHz ~0.4 mJy at 21.2 GHz We find no evidence for any radio emission at the position of the optical transient (Coulter et al. LVC GCN 21529). Analysis of the full dataset is underway. Subsequent epochs are planned. Thank you to CSIRO staff for supporting these observations. -- Keith Bannister //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21560 SUBJECT: LIGO/Virgo G298048: SkyMapper uvgri photometry of the candidate in NGC 4933 DATE: 17/08/18 13:54:11 GMT FROM: Seo-Won Chang at ANU C. Wolf, S.W. Chang, A. Mller (ANU) We report photometry of the optical source in NGC 4993 reported by Coulter et al. (LVC GCN 21529), Allam et al. (LVC GCN 21530), Yang et al. (LVC GCN 21531), Melandri et al. (LVC GCN 21532) in response to LIGO/Virgo GW trigger G298048 (LVC, GCN 21513). The source at RA = 13:09:48.09 DECL. = -23:22:53.35 was observed with the 1.35-m ANU SkyMapper telescope at Siding Spring Observatory on the night of 2017-08-18 from 10:00:00 to 10:09:40 UTC. Initial photometry for the candidates AB magnitude is: u-band (350/40) = 17.9 +/- 0.15, v-band (384/28) = 17.9 +/- 0.10, g-band (510/156) = 17.76 +/-0.05, r-band (617/156) = 17.20 +/-0.05 and i-band (779/140) = 16.0 +/- 0.30. Note that the u-band is uncertain because the frames were taken at airmass 2.5 to 2.7, and the i-band is highly uncertain due to a rudimentary host subtraction. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21561 SUBJECT: LIGO/Virgo G298048: Subaru HSC z-band photometry of the possible optical counterpart DATE: 17/08/18 14:27:26 GMT FROM: Nozomu Tominaga at Konan U Yoshida, M., Tanaka, M., Terai, T., Nakata, F., Furusawa, H., Koshida, S. (NAOJ), Utsumi, Y., Kawabata K. S. (Hiroshima Univ.), Tominaga, N. (Konan Univ.), Motohara, K., Ohsawa, R., Morokuma, T., Yasuda, N. (Univ. of Tokyo), Kawai, N. (Tokyo Tech) on behalf of the J-GEM collaboration As reported in Yoshida et al. 2017 (GCN 21549), we performed z-band imaging observations for the gravitational wave event G298048 (GCN 21505; 21509; 21513) with Hyper Suprime-Cam attached to the Subaru telescope on August 18 2017 UT. The survey fields include SSS17a (RA = 13:09:48.09 DECL. = -23:22:53.35, Coulter et al. 2017; GCN 21529) possibly associated with G298048. After photometric calibration with Pan-STARRS1 catalog (Chambers et al. 2016) using HSC pipeline (Bosch et al. 2017), we obtained psf magnitude of z = 17.3, which is consistent with the magnitudes reported by Chambers et al. (GCN 21553). We did not find a significant variability with > 0.1 mag during our observations from 5:16 UT until 5:40 UT. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21562 SUBJECT: LIGO/Virgo G298048: ASKAP search for fast radio bursts DATE: 17/08/18 14:36:00 GMT FROM: Keith Bannister at ATNF K. Bannister (CSIRO), R. Shannon (CSIRO/Curtin/ICRAR), A. Hotan (CSIRO), C. James (Curtin), J-P Macquart(Curtin/ICRAR), S. Oslowski (Swinburne), W. Farah (Swinburne) on behalf of the ASKAP collaboration. We observed the 90% containment region of the Bayestar map (Singer et al. LVC GCN 21513) with 7 antennas of the The Australian Square Kilometer Array Pathfinder (ASKAP). We recorded fast autocorrelation data with 336 x 1 MHz channels and a time sampling of 1.26 ms centered at 1320 MHz (see [1] for observing details). We used flys-eye observing mode, with some parts of the field covered by 2 antennas and some by 1 antenna. We had 2 observing runs starting roughly 16h after the gravitational wave trigger: Run 1: 2017-08-18 04:05:35 to 2017-08-18 07:44:56 UT Run 2: 2017-08-18 08:57:33 to 2017-08-18 13:02:20 UT We are searching the data for fast radio bursts. [1] Bannister et al. 2017, ApJL, 841, 12 -- Keith Bannister //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21563 SUBJECT: LIGO/Virgo G298048: Observation of the potential optical counterpart in NGC 4993 DATE: 17/08/18 14:45:33 GMT FROM: Myungshin Im at Seoul National U M. Im, C. Choi, J. Kim, H. M. Lee (SNU), S.-L. Kim (KASI) on behalf of the KU collaboration We imaged SSS17a in NGC 4993 (Coutler et al. LVC GCNs 21529), the potential optical counterpart of LIGO/Virgo G298048 (LVC GCNs 210505, 21509, 21513) with the g, r, i, z and an array of medium-band filters. The observation was carried out using two 0.43m telescopes, LSGT and T17 of iTelescope.Net at the Siding Spring Observatory (Im et al. 2015, JKAS, 48, 207). The observation started at 2017-08-18 09:47 (UT), and continued for about 30 min until the weather stopped the osbservation. SSS17a is clearly visible in the images taken. Further analysis of the data is ongoing. Additional observations are ongoing/planned using these telescopes and the KMTNet 1.5m telescopes in the coming nights. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21564 SUBJECT: LIGO/Virgo G298048: AGILE-GRID analysis of the potential counterpart field DATE: 17/08/18 15:22:43 GMT FROM: Francesco Verrecchia at ASDC, INAF-OAR A. Bulgarelli (INAF/IASF-Bo), M. Tavani (INAF/IAPS, and Univ. Roma Tor Vergata), F. Verrecchia (SSDC and INAF/OAR), M. Cardillo, G. Piano (INAF/IAPS), M. Pilia (INAF/OA-Cagliari), C. Pittori (SSDC and INAF/OAR), I. Donnarumma (ASI), F. Longo (Univ. Trieste and INFN Trieste), A. Ursi, G. Minervini, A. Argan, Y. Evangelista (INAF/IAPS), F. Lucarelli (SSDC and INAF/OAR), N. Parmiggiani, A. Zoli, V. Fioretti, F. Fuschino (INAF/IASF-Bo), A. Trois (INAF/OA-Cagliari), M. Marisaldi (INAF/IASF-Bo and Bergen University), A. Giuliani (INAF/IASF-Mi), report on behalf of the AGILE Team: As reported in previous GCNs of the AGILE Team (LVC GCN 21525 and 21526) at the G298048 event time T0 the 90% localization region (LR) of the HLV skymap was not accessible to AGILE detectors because of a prolonged Earth occultation of that portion of the sky. AGILE is currently spinning and is scanning about 80% of the entire sky every 7 minutes. The G298048 HLV LR was exposed before and after T0 with a complex pattern that depends on the instrument boresight revolution and Earth occultation. In the analysis results reported below, we use the updated G298048 sky map (LVC GCN 21527) including the optical transient SSS17a (RA = 13:09:48.09 DECL. = -23:22:53.35, Coulter et al. 2017; LVC GCN 21529) which is the potential optical counterpart (see also Allam et al. LVC GCN 21530, Yang et al. LVC GCN 21531, Melandri et al. LVC GCN 21532) to G298048. The closest in time AGILE-GRID detector exposure of the G298048 LR starts near T0+950 sec. For an integration time ranging from T0+950 to T0+1100 sec, we obtained the 3-sigma gamma-ray flux upper limit UL_1 = 5.7e-08 erg cm^2 s^-1 at energies above 100 MeV at the optical transient location. Previously, the closest in time passage of the AGILE-GRID instrument over the LR occurred at times from T0-1950 to T0-1750 sec before T0. For this exposure we obtained the 3-sigma gamma-ray flux upper limit UL_2 = 3.4e-08 erg cm^2 s^-1 at energies above 100 MeV at the optical transient location. We also carried out an analysis on longer timescales. For an integration time during a 10 ksec time window preceding T0, we obtain an AGILE-GRID gamma-ray flux upper limit of UL_3 = 2.8e-09 erg cm^-2 s^-1 at the optical transient location at energies above 100 MeV. For an integration time of 10 ksec following T0, we obtain UL_4 = 3.5e-09 erg cm^-2 s^-1 at energies above 100 MeV at the optical transient location. No significant new sources were found in our analysis. Additional analysis of AGILE data is ongoing. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21565 SUBJECT: LIGO/Virgo G298048: Brightening of Possible Counterpart DATE: 17/08/18 15:58:41 GMT FROM: Iair Arcavi at LCOGT I. Arcavi, D. A. Howell, C. McCully, G. Hosseinzadeh, S. Vasylyev (UCSB/Las Cumbres Obs), M. Zalzman, D. Poznanski (TAU), L.P. Singer (NASA/GSFC), S. Valenti (UC Davis), T. Piran (HUJI), D. Kasen, J. Barnes (UC Berkeley), W. Fong (Northwestern) and D. Maoz (TAU) report the brightening of SSS17a / DLT17ck, the possible optical counterpart reported by Coulter et al. (LVC GCN 21529), Allam et al. (LVC GCN 21530), Yang et al. (LVC GCN 21531), Melandri et al. (LVC GCN 21532) and others. In the course of Las Cumbres Observatory LIGO followup we observed NGC 4993 from our 1-meter telescopes at the Cerro Tololo Inter-American Observatory in Chile at 2017-08-18 00:15 UT (Arcavi et al.; LCV GCN 21538) and at the Siding Spring Observatory in Australia at 2017-08-18 09:10 UT. Both images were taken in the broad w (=g+r+i) filter. Preliminary aperture photometry, comparing to 7 nearby stars, indicates a relative increase in brightness of the candidate by 0.11 magnitudes (with an uncertainty of 0.03 magnitudes) in the ~9 hours between the first and second epochs. Further observations and analysis are ongoing. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21566 SUBJECT: LIGO/Virgo G298048: Moderate dimming or no brightening of the optical counterpart candidate? DATE: 17/08/18 17:15:43 GMT FROM: Myungshin Im at Seoul National U M. Im, C. Choi, J. Kim, H. M. Lee (SNU), S.-L. Kim (KASI) on behalf of the KU collaboration We analyzed the medium-band data we took for SSS17a at the Siding Spring Observatory at 2017-08-18.4 (UT) in Im et al. (LVC GCN 21563). The preliminary magnitude at the medium-band filter m475 centered at 475nm (Choi & Im JKAS, 50, 71) is m475 = 17.5 +- 0.2 AB mag, somewhat brighter than g ~ 17.9 mag of Wolf et al. (LVC GCN 21560) taken at the same site at a similar time. Considering that m475 is similar to the g-band filter, this prefers a moderate dimming in comparison to g=17.2 +- 0.1 mag at the time of 2017-08-18.1 (UT) from Simon et al. (LVC GCN 21551) to a brightening as suggested by Arcavi et al. (LVC GCN 21565). However, currently, the large uncertainties in the magnitude estimates (mostly due to host galaxy subtraction problem) makes us difficult to rule out no brightening or even a slight brightening of the EM counterpart candidate. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21567 SUBJECT: LIGO/Virgo G298048: Correction to Swope photometry announced in LVC GCN 21529 DATE: 17/08/18 17:19:22 GMT FROM: Ryan Foley at UCSC D. A. Coulter, C. D. Kilpatrick, M. R. Siebert, R. J. Foley (UCSC), B. J. Shappee, M. R. Drout, J. S. Simon, and A. L. Piro (Carnegie) on behalf of the One-Meter Two-Hemisphere (1M2H) collaboration: We report a correction to the photometric magnitude of SSS17a announced in LVC GCN 21529. After re-examination of the imaging and using 97 APASS i' standards for relative photometry, we conclude that the source had a brightness of i = 17.3 +/- 0.1 mag at the time of observation on UT 2017-08-17.98. We apologize for the error. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21568 SUBJECT: LIGO/Virgo G298048: UPDATE on IceCube neutrino candidates --- no coincidence with newest GW skymap DATE: 17/08/18 17:27:25 GMT FROM: Stefan Countryman at LIGO Scientific Collaboration I. Bartos, S. Countryman (Columbia), C. Finley (U Stockholm), E. Blaufuss (U Maryland), R. Corley, Z. Marka, S. Marka (Columbia) on behalf of the IceCube Collaboration In GCN 21511 (an update to GCN 21508) we reported the identification of a neutrino candidate coincident with preliminary LIGO GW skymaps using only LHO data (GCN 21509), and Fermi GBM's preliminary skymaps (GCN 21506). This neutrino candidate is *not in the 90% credible region of the latest GW skymap* incorporating LHO, LLO, and Virgo data (GCN 21513). The updated joint GW/High Energy Neutrino skymap is available on GraceDB at . A JSON-formatted list of the temporally coincident neutrinos included in the joint plot is available at . //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21569 SUBJECT: LIGO/Virgo G298048: Additional Gemini-South acknowledgements DATE: 17/08/18 17:44:26 GMT FROM: Leo Singer at NASA/GSFC L. P. Singer (NASA/GSFC) reports on behalf of the Global Relay of Observatories Watching Transients Happen (GROWTH) collaboration: In GCN 21552, our acknowledgement of the Gemini-South staff was incomplete. We additionally thank the following Gemini staff: the telescope operator was Ariel Lopez, the observers were Karleyne Silva and Gonzalo Diaz, and the queue coordinator for this week and the contact scientist for our program is Hwihyun Kim. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21570 SUBJECT: LIGO/Virgo G298048: New MASTER observations of the OT in NGC 4993 DATE: 17/08/18 18:06:51 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs V.M. Lipunov, E. Gorbovskoy, V.G.Kornilov, N.Tyurina, V.Shumkov, D.Kuvshinov, P.Balanutsa, O.Gress, A.Kuznetsov, M.I.Panchenko, A.V.Krylov, I.Gorbunov Lomonosov Moscow State University, Sternberg Astronomical Institute R.Podesta, C.Lopez, F. Podesta Observatorio Astronomico Felix Aguilar (OAFA) , National University of San Juan, Argentina H. Levato, C. Saffe Instituto de Ciencias Astronomicas,de la Tierra y del Espacio (ICATE), San Juan, Argentina N.M. Budnev, O. Gress, K. Ivanov, S.Yazev Irkutsk State University V.Yurkov, Yu.Sergienko, A.Gabovich Blagoveschensk Educational State University, Blagoveschensk D.Buckley, S. Potter, M. Kotze, South African Astronomical Observatory R. Rebolo, M. Serra-Ricart, G. Israelian, N.Lodiu The Instituto de Astrofisica de Canarias A. Tlatov, V.Sennik Kislovodsk Solar Station of the Pulkovo Observatory As we reported in LVC GCN 21546 MASTER-OAFA have imaged the BAYESTAR localization map of LIGO/Virgo G298048 (GCN 21513). MASTER-SAAO have new images of NGC 4993 galaxy starting 2017-08-18 17:06:55 UT in B, R and unfiletred with magnitude limit 19.8. We see object in B and unfiltered images detected by Coulter et al. (LVC GCN 21529), Allam et al. (LVC GCN 21530), Yang et al. (LVC GCN 21531), Melandri et al. (LVC GCN 21532), Lipunov et al., (LVC GCN 21546). The OT is not essentially changed during last ~24 hours. This message can be citted. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21571 SUBJECT: LIGO/Virgo G298048: Archival VLA observations DATE: 17/08/18 18:16:30 GMT FROM: Kate Alexander at Harvard U P. K. G. Williams (Harvard), K. D. Alexander (Harvard), and E. Berger (Harvard) report on behalf of a larger collaboration: We investigated observations of the candidate optical counterpart to LIGO/Virgo trigger G298048 in the NRAO Very Large Array (VLA) data archive. The field containing the candidate was observed at both 1.51 GHz ("L band") and 4.89 GHz ("C band") on June 10 and 23, 1984, as part of program AW0110. The on-source integration times were 11.5 and 5.5 minutes, respectively. We obtained images generated by the NRAO's VLA/AIPS data calibration pipeline (L. Sjouwerman, in preparation), which automatically processed the data in 2009. We see no persuasive evidence for radio emission at the location of either the host galaxy or the counterpart candidates. We measure image RMS values of ~180 and ~340 microJy near the candidates in the 1.51 and 4.89 GHz images, respectively. Taking a flux density upper limit of three times the RMS and a luminosity distance of 39.5 Mpc, these values correspond to upper limits on the spectral luminosity of 10^27.0 and 10^27.3 erg/s/Hz at 1.51 and 4.89 GHz. Using the relation between synchrotron emission and star formation rate presented by Yun & Carilli (2002 ApJ 568 88), the implied star formation rate of the candidate host galaxy is less than 0.05 solar masses per year. For comparison, Alexander et al. (LVC GCNs 21545, 21548) report a VLA radio detection of 300 microJy at 9.77 GHz, and Bannister et al. (LVC GCN 21559) report ATCA radio detections of 600-400 microJy at 8.5--21.2 GHz. These values are consistent with the archival limits. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21572 SUBJECT: LIGO/Virgo G298048: Continued Swift UV and X-ray Monitoring of SSS17a DATE: 17/08/18 18:32:37 GMT FROM: Brad Cenko at NASA/GSFC S. B. Cenko (NASA/GSFC), S.W.K. Emery (UCL-MSSL), S. Campana (INAF-OAB),P.A. Evans (U. Leicester), J.A. Kennea (PSU), A.A. Breeveld (UCL-MSSL), E. Troja(NASA/GSFC/UMCP), P.T. O'Brien (U. Leicester), S.D. Barthelmy(NASA/GSFC), A.P. Beardmore (U. Leicester), D.N. Burrows (PSU), G. Cusumano (INAF-IASF PA), A. D'Ai (INAF-IASFPA), P. D'Avanzo (INAF-OAB),V.D'Elia(ASDC), P. Giommi (ASI), C. Gronwall(PSU), H.A. Krimm (CRESST/GSFC/USRA), N.P.M. Kuin (UCL-MSSL), A.Y. Lien(GSFC/UMBC), F.E. Marshall (NASA/GSFC), A. Melandri (INAF-OAB), J.A.Nousek (PSU), S.R. Oates (U. Warwick), J.P. Osborne (U. Leicester), C.Pagani (U. Leicester), K.L. Page (U.Leicester), D.M. Palmer (LANL), M.Perri (ASDC), J.L. Racusin (NASA/GSFC), B. Sbarufatti (INAF-OAB/PSU),M.H. Siegel (PSU), G. Tagliaferri (INAF-OAB), A. Tohuvavohu (PSU) reporton behalf of the Swift team: We obtained a second epoch of UV and X-ray imaging of SSS17a (Coulter et al.; GCN 21529), the candidate optical counterpart of G298048 (LVC; GCN 21509) with the Swift Gamma-Ray Burst Explorer. Observations beganat 13:30 UTon 2017August 18. Compared with our previous epoch of imaging (Evans et al.; GCN 21550), the source has faded significantly at UV wavelengths. Specifically we measure the following magnitudes (with no host subtraction): Filter T_start(s) T_stop(s) Exp(s) Mag (Vega) u 90029 90164 13317.42 +/- 0.09 uvw189755 90024 26518.50 +/- 0.15 uvm289346 94665 104520.40 +/- 0.27 uvw290170 90674 49620.37 +/- 0.32 Given the relatively flat evolution in the optical and NIR, this suggests significant cooling in the source. The source remains undetected in the X-rays, with comparable limits to our previous epoch. Further observations are planned. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21574 SUBJECT: LIGO/Virgo G298048: ATCA upper limits on radio emission from optical source SSS17a in NGC 4993 DATE: 17/08/18 20:19:00 GMT FROM: David Kaplan at UW-Milwaukee D. Kaplan (UWM), T. Murphy (University of Sydney), K. Bannister (CSIRO), C. Lynch (University of Sydney), D. Dobie (University of Sydney) on behalf of the VAST collaboration. Following Bannister et al. (LVC GCN 21559), who reported ATCA detections of a radio source consistent with the position of NGC 4993 that is also seen with the VLA (Alexander et al. LVC GCN 21548), we present upper limits to the radio emission of any source at the position of the potential optical counterpart, SSS17a (Coulter et al., LVC GCN 21529). We fit and subtracted a point-source at the optical position of NGC 4993 (13:09:47.706, -23:23:01.79; Skrutskie et al. 2003, 2MASS Extended Source Catalog). The flux densities were consistent with the values reported by Bannister et al. (LVC GCN 21559). We then measured the rms noise at the position of SSS17a as well as 3 other source-free positions nearby. In all cases there was no detectable emission at the position of SSS17a (9.9 arcsec away), and the noise was essentially identical across all positions. Assuming that all of the emission originates with the center of NGC 4993, our flux density for the galaxy and 3-sigma upper limits to emission at the position of SSS17a are: Frequency NGC 4993 Flux Density 3-sigma Limit for SSS17a 8.5 GHz: 0.66 mJy 120 uJy 10.5 GHz: 0.54 mJy 150 uJy 16.7 GHz: 0.42 mJy 130 uJy 21.2 GHz: 0.34 mJy 140 uJy Thank you to CSIRO staff for supporting these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21575 SUBJECT: LIGO/Virgo G298048: Archival 2MASS and Spitzer non-detections of the potential LIGO EM counterpart SSS17a DATE: 17/08/18 20:23:05 GMT FROM: Stephen Eikenberry at U of Florida S. Eikenberry, K.Ackley, and S. Klimenko (U. Florida) report: We have investigated archival 2MASS (28 Apr 1998) and Spitzer (12 Oct 2014) infrared observations of the field of SSS17a (Coulter et al. LVC GCN 21529). We find no evidence of a point-like source at this location. While the presence of the host galaxy somewhat complicates sensitivity estimates, in the case of 2MASS we have a preliminary estimate for a 3-sigma upper limit of J(Vega) ~ 17.6 +- 0.2 mag, which corresponds to J(AB) ~ 18.5 +- 0.2 mag. This is a factor of ~2.5 fainter than the J(AB)=17.5 mag detection of Tanvir et al. (LVC GCN 21544), indicating a variable or transient nature for this source. More detailed analyses of the upper limits for both 2MASS and Spitzer are forthcoming. [GCN OPS NOTE(18aug17): Per submitter's and author's request, the submitter was changed from Singer to Eikenberry. Singer submitted as Eikeberry's proxy, because Eikenberry's GCN account was not yet activated.] //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21576 SUBJECT: LIGO/Virgo G298048: prior photometry from VISTA Hemisphere Survey DATE: 17/08/18 21:16:32 GMT FROM: Nial Tanvir at U of Leicester N. R. Tanvir (U. Leicester), A. J. Levan, D. Steeghs (U. Warwick) report: We note that the field of NGC 4993 was observed as part of the VISTA Hemisphere Survey on 9 April 2014. No source is visible at the location of the candidate counterpart (Coulter et al. LVC GCN 21529). We obtain a 3-sigma upper limit of J(AB)=21.6, significantly fainter than the provisional magnitude of J(AB)=17.5+/-0.1 reported for the infrared transient (Tanvir et al. LVC GCN 21544). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21577 SUBJECT: LIGO/Virgo G298048: optical spectral energy distribution of SSS17a DATE: 17/08/18 23:00:31 GMT FROM: Daniele Malesani at DARK/NBI Daniele Malesani, Darach Watson, and Jens Hjorth (all DARK/NBI), report: Analysis of the optical and near-infrared data reported through the GCNs allows to build the spectral energy distribution of the candidate optical counterpart (Coulter et al., GCN 21529; Allam et al., GCN 21530; Yang et al., GCN 21531) of the LIGO/Virgo event G298048 (GCN 21509). A standard Galactic extinction curve with A_V = 0.34 has been adopted but no rest-frame extinction has been included. We caution that the available data are based on a preliminary analysis and are not always strictly simultaneous, though the reported variability (at least in the optical) is modest (Arcavi et al., GCN 21565). Overall, the SED shows a blue continuum in the NIR to optical region, reaching a peak around the g band and rapidly decreasing in the UV as constrained by the Swift/UVOT measurements (Evans et al., GCN 21550). The spectral slope in the UV is quite steep, being well represented by an exponential tail or a very steep power law (spectral index ~3.7 on Aug 18.16 UT; and ~ 5 on Aug 18.57 UT). A blackbody with T ~ 8500 K broadly represents the available data at a mean epoch Aug 18.1 UT (black line in the plot). Assuming an isotropic, spherically symmetric emitter, the radius of the blackbody source would be approximately 10^15 cm for a distance of 40 Mpc. At 55 ks after the explosion, this would imply a relativistic expansion velocity. As noted by Cenko et al. (GCN 21572), the later Swft/UVOT measurement indicate cooling in the source, implying further expansion and confirming the relativistic velocity. The SED is clearly atypical for optical afterglows of long and short GRBs, as also highlighted by the lack of detection in the X-ray band (Evans et al., GCN 21550). A plot showing the counterpart SED is posted online at: http://www.astro.ku.dk/~malesani/GRB/170817A/SED_opt.png Data were grouped in quasi-simultaneous sets and were collected from the following reports: - Aug 18.0 UT (red triangles): Yang et al. (GCN 21531); Nicholl et al. (GCN 21541); Tanvir & Levan (GCN 21544); Simon et al. (GCN 21551); Singer et al. (GCN 21552); - Aug 18.16 UT (blue circles): Evans et al. (GCN 21550); - Aug 18.42 UT (green squares): Wolf et al. (GCN 21560); - Aug 18.57 UT (cyan diamonds): Cenko et al. (GCN 21572). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21578 SUBJECT: LIGO/VIRGO G298048: Expansion Velocity of SSS17a Consistent With Relativistic Merger Ejecta DATE: 17/08/18 23:11:30 GMT FROM: Philip Cowperthwaite at Harvard U P.S. Cowperthwaite (Harvard), M. Nicholl (Harvard), E. Berger (Harvard) We construct a preliminary UV/Optical/NIR SED for the potential optical counterpart SSS17a first reported by Coulter et al. (GCN 21529). These data are compiled from the photometry reported in circulars submitted during the first night of follow-up. We correct these data for extinction due to reddening along the line of sight to the host galaxy NGC 4993. We perform a preliminary fit with a blackbody function to this SED finding an effective temperature of T = 8000 K and an effective radius of R = 6e14 cm. We test the sensitivity of our fit to the UV flux, refitting with the Swift/UVOT data excluded. We find T = 10,200 K and R ~ 4e14 cm. In both cases, the large expansion radius and short time since explosion (t ~ 1 day) suggest an expansion velocity of >0.2c. This is too fast to be explained by supernova ejecta, but is consistent with the expansion velocities expected for relativistic BNS/NS-BH merger ejecta. These values, and the inferred relativistic expansion, are consistent with the results of Malesani et al. (GCN 21577). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21579 SUBJECT: LIGO/Virgo G298048: Continued observation for DLT17ck DATE: 17/08/19 00:18:04 GMT FROM: Sheng Yang at UC Davis Sheng Yang (INAF-OAPd, UC Davis), Stefano Valenti(UC Davis), David Sand (UA), Leonardo Tartaglia (UA, UC Davis), Enrico Cappellaro(INAF-OAPd), Dan Reichart, Josh Haislip (UNC) report on behalf of the Gravitational Wave Follow-Up by DLT40. We report the second epoch for DLT17ck/SSS17a, the possible counterpart of G298048 in NGC 4993 detected by Coulter et al. (LVC GCN 21529), Allam et al. (LVC GCN 21530), Yang et al. (LVC GCN 21531), Melandri et al. (LVC GCN 21532), Arcavi et al. (LVC GCN 21538), Lipunov et al., (LVC GCN 21546). Using data from the PROMPT 5 0.41m telescope located at CTIO, DLT40 observation began at 2017 August 18.99 UT and shows the source at magnitude R = 18.00 +/- 0.06 mag. Compared with our discovery detections, R~17.3 mag in Yang et al. (LVC GCN 21531), the source is declining. We also report last our non-detection at 2017 July 27.99 UT, during the monitoring of NGC4993 with the DLT40 search. The magnitude limit is up to 19.1 mag (open filter scaled to r band). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21580 SUBJECT: LIGO/Virgo G298048: Observed fading of optical counterpart SSS17a DATE: 17/08/19 00:22:23 GMT FROM: Philip Cowperthwaite at Harvard U M. Nicholl (Harvard), P. S. Cowperthwaite (Harvard), E. Berger (Harvard), P. K. G. Williams (Harvard), S. Allam (Fermilab), J. Annis (Fermilab), J. Garcia Bellido (IFT CSIC/UAM), D. J. Brout (UPenn), D. Brown (Syracuse), R. E. Butler (Fermilab), H.-Y. Chen (Harvard), R. Chornock (Ohio University), E. Cook (TAMU), , H. T. Diehl (Fermilab), A. Drlica-Wagner (Fermilab), Z. Doctor (U. Chicago), M. R. Drout (Carnegie), B. Farr (U Chicago), R. J. Foley (UCSC), W. Fong (Northwestern), D. Fox (Penn State), J. Frieman (Fermilab/UChicago), M.S.S. Gill (Stanford), R. Gruendl (NCSA), K. Herner (Fermilab), D. Holz (UChicago), R. Kessler (UChicago), H. Lin (Fermilab), J. Marriner (Fermilab), R. Margutti (Northwestern), J. Marshall (TAMU), E. Neilsen (Fermilab), F. Paz-Chincon (NCSA), A. Rest (STScI), M. Sako (UPenn), D. Scolnic (KICP), N. Smith (Arizona), M. Soares-Santos (BrandeisU), D. Tucker (Fermilab), V. A. Villar (Harvard), A. Walker (NOAO), B. Yanny (Fermilab), P. Lopes (UFRJ), F. Durret (IAP), A. Lourenço (UFRJ) On behalf of the DESGW+community team: We report further i- and z-band photometry from DECam imaging of the possible optical counterpart to G298048 first identified in Coulter et al. (LVC GCN 21529), and further reported on by Allam et al. (LVC GCN 21530), Valenti et al. (LVC GCN 21531), Melandri et al. (LVC GCN 21532) and Arcavi et al. (GCN 21538). Observations were obtained on 2017-08-19 at 23:23 UTC. We find preliminary PSF magnitudes of i = 17.8 +/- 0.1 mag z = 17.6 +/- 0.1. mag In images obtained the previous night (2017-08-18 at 00:04 UT), we measured i ~ z ~ 17.5 mag (Nicholl et al., LVC GCN 21541). This indicates a fading of ~0.3 mag in i-band over the course of 1 day. This value is consistent with that expected for an afterglow or rapidly-evolving kilonova. These magnitudes are determined from differential PSF photometry of DECam images relative to Pan-STARRs 3pi catalogs. Further analysis is ongoing. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21581 SUBJECT: LIGO/Virgo G298048: Rapid Evolution of Possible Counterpart DATE: 17/08/19 01:26:07 GMT FROM: Iair Arcavi at LCOGT I. Arcavi, D. A. Howell, C. McCully, G. Hosseinzadeh, S. Vasylyev (UCSB/Las Cumbres Obs), D. Poznanski, M. Zalzman (TAU), L.P. Singer (NASA/GSFC), S. Valenti (UC Davis), T. Piran (HUJI), D. Kasen, J. Barnes (UC Berkeley), W. Fong (Northwestern) and D. Maoz (TAU) report the sudden fading of SSS17a / DLT17ck, the possible optical counterpart reported by Coulter et al. (LVC GCN 21529) and others. In the course of Las Cumbres Observatory LIGO followup we have now accumulated four epochs of the possible counterpart SSS17a / DLT17ck in the last 24 hours from our telescopes in the Cerro Tololo Inter-American Observatory (Chile), the Siding Spring Observatory (Australia) and the South African Astronomical Observatory (South Africa). Using aperture photometry in the wide w-band (=g+r+i), we see the transient first brighten by 0.12 magnitudes (as reported in Arcavi et al. LVC GCN 21565) and then fade by ~0.2 magnitudes: Time (UT) Site Relative w-band Magnitude 2017-08-18 00:15 Chile 0 2017-08-18 09:10 Australia -0.12 +- 0.02 2017-08-18 17:35 South Africa +0.19 +- 0.04 2017-08-18 23:13 Chile +0.22 +- 0.13 Further observations (including other bands) and analysis are ongoing. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21582 SUBJECT: LIGO/VIRGO G298048: ePESSTO optical spectra of the candidate optical/NIR counterpart of the gravitational wave G298048 in NGC4993. DATE: 17/08/19 01:46:26 GMT FROM: S. J. Smartt at Queens U Belfast J. Lyman (Univ. of Warwick), D. Homan (Univ. of Edinburgh), K. Maguire (QUB), M. T. Botticella (INAF-Capodimonte), M. Fraser (UCD), C. Inserra (Southampton), E. Kankare (QUB), S. J. Smartt (QUB), K. W. Smith (QUB), M. Sullivan (Southampton), S. Valenti (UC Davis), O. Yaron (Weizmann), I. Manulis (Weizmann), D. Young (QUB), T.-W. Chen (MPE), S. Campana (INAF-Brera), S. Benetti, L. Tomasella (INAF-Padova), G. Leloudas (DARK, Copenhagen), Z. Cano (IAA, Granada). Under the extended Public extened ESO Spectroscopic Survey for Transient Objects (ePESSTO; see Smartt et al. 2015, A&A, 579, 40 http://www.pessto.org), we report spectra of the optical/NIR candiate counterpart of the gravitational wave source G298048 in NGC4993. This object was discovered by Coulter et al. (GCN 21529, named SSS17a) and further detected by Allam et al. (GCN 21530), Yang et al. (GCN 21531), Melandri et al. (GCN 21532), Nicholl et al. (GCN21541), Tanvir & Levan (GCN21544), Chambers et al. (GCN 21553), Yoshida et al. (GCN 21549). The observations were performed on the ESO New Technology Telescope at La Silla with the EFOSC2 instrument in spectroscopic mode starting from 2018-08-18 at 23:20 UT, using the Gr11 and Gr16 which provide coverage 3345-9995 at a resolution between 260-396 (v = 1150 - 756 km/s) for a 1.5" slit, which was used in roughly 1.5-2.0" seeing. Quick look reductions (not including fringe and flat correction) indicate the spectrum is highly unusual for a nearby transient. We have dereddening the spectrum with A_v = 0.34, for Milky Way correction. The continuum is featureless, similar to the report of the first Magellan spectrum in Drout et al. (GCN 21547). But it peaks at 5500 and falls off rapidly in the blue. This is consistent with the Swift colours reported and the fading U-band and UV flux. The red part (beyond 5000Angs) can be fit with a black-body temperature of around 6000K or a power law. But neither are consistent with the turn over in the blue. There are no strong features in the blue that indicate line absorption or could be identified with known transitions. There are no Balmer lines, no Ca II H&K, or Si II absorption seen in supernova-like transients. We can certainly conclude this is not a young supernova of any type in this host, nor is it consistent with being a background supernova of any standard type. The UV dimming and maintaining of the red and NIR flux appears broadly consistent with many flavours of kilonova models. Further observations with ePESSTO will continue over the next 4 nights, combining EFOSC2 and SOFI observations. During the 5 years of PESSTO spectroscopic surveys, this transient stands out as exceptional in its colours, evolution and spectra (supporting the ideas in Foley GCN 21557). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21583 SUBJECT: LIGO/Virgo G298048: Additional Swope Observations of SSS17a DATE: 17/08/19 01:54:36 GMT FROM: Ryan Foley at UCSC C. D. Kilpatrick, D. A. Coulter, M. R. Siebert, R. J. Foley (UCSC), B. J. Shappee, M. R. Drout, J. S. Simon, A. L. Piro (Carnegie), A. Rest (STScI) report on behalf of the One-Meter Two-Hemisphere (1M2H) collaboration: We obtained imaging in B, V, and i bands of SSS17a (Coulter et al., LVC GCN 21529) on 2017 Aug 19 UT with the 1-m Swope telescope at Las Campanas Observatory. We calibrated these data using approximately 90 B, V, and i' APASS standards in the same field as SSS17a and report the following preliminary photometry: B = 18.8 mag +/- 0.1 mag V = 18.1 mag +/- 0.1 mag i = 17.4 mag +/- 0.1 mag Additional photometry is being obtained and analyzed. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21584 SUBJECT: LIGO/Virgo G298048: GROND photometry of candidate optical counterpart reveals brightening in the NIR DATE: 17/08/19 01:58:14 GMT FROM: Philip Wiseman at MPE/Garching P. Wiseman, T.-W. Chen, J. Greiner, and P. Schady (all MPE Garching) report on behalf of the GROND team: We observed the field of the of the transient source SSS17a in NCG 4993 (RA = 13:09:48.09 DEC = -23:22:53.35, Coulter et al. GCN #21529, Allam et al. GCN #21530, Yang et al. GCN #21531, Melandri et al. GCN #21532), possibly associated with LIGO/Virgo trigger G298048, simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008,PASP 120, 405) mounted at the 2.2 m MPG telescope at ESO La Silla Observatory(Chile). Observations started at 23:15 UT on August 18th 2017. They were performed at an average seeing of 1.8" and at an average airmass of 1.4. We clearly detect a single point source at the location of the transient, although the strong host contribution hinders photometric accuracy. Based on the first 13.8 min of total exposures in g'r'i'z' and 12.4 min in JHK, we estimate preliminary magnitudes (all in AB system) of g' = 17.9 +/- 0.1 mag, r' = 17.2 +/- 0.1 mag, i' = 17.2 +/- 0.1 mag, z' = 16.8 +/- 0.1 mag, J = 16.6 +/- 0.2 mag, H = 16.9 +/- 0.2 mag, and K = 16.8 +/- 0.2 mag. There appears to be little change in the optical brightness of the source: we compare our magnitudes to the g = 17.76 mag and r = 17.20 mag from 14 hours previous,reported by SkyMapper (Wolf et al. GCN #21560); and to the i,z = 17.25 mag of Pan-STARRS (Chambers et al. GCN #21553) and z = 17.3 from HSC-z (Yoshida et al. GCN #21561) from 19 hours previous. On the other hand, the object has brightened significantly in the NIR over the last 24 hours. We compare the J band to the value of 17.5 mag (AB) from VISTA/VIRCAM reported by Tanvir et al. (GCN #21544), while the K band (now 14.9 in Vega) is much brighter than the 16.9 mag (Vega) reported by Singer et al. (GCN #21552). Given magnitudes are calibrated against Pan-STARRS zeropoints/2MASS field stars and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of E_(B-V)= 0.1 mag in the direction of the candidate (Schlafly & Finkbeiner 2011). After the Milky Way extinction correction, we fitted our colour SED assuming a black body (no K-correction applied), which indicates a temperature of 5333 +/- 243 K. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21585 SUBJECT: LIGO/Virgo G298048: Possible features in the spectrum of GW counterpart SSS17a DATE: 17/08/19 03:10:19 GMT FROM: Matt Nicholl at Harvard-Smithsonian/CfA M. Nicholl (Harvard), C. Briceno (CTIO), P. Cowperthwaite (Harvard), E. Berger (Harvard), J. Elias (NOAO), S. Heathcote (CTIO), J. Annis (Fermilab), D. Tucker (Fermilab), M. Soares-Santos (Brandeis), R. Kessler (U Chicago), M Sako (U Penn) We report optical spectroscopy of SSS17a, the counterpart to G298048, using the Goodman Spectrograph on the 4m SOAR telescope on 2017-08-18 starting at UT 23:23:38. This is ~1.5 days after the LIGO and Fermi signals. Previous spectra were obtained by Drout et al (GCN 21547) and more recently Lyman et al (GCN 21582). We confirm some of the results of Lyman et al: a peak between 5000-6000 Angs, rapid fall-off in the blue, and no match to known supernova types. The colour temperature is best matched by a blackbody with T~5000K, after dereddening by a Milky Way E(B-V)=0.1053. The UV flux appears suppressed relative to a simple blackbody. This shows significant cooling compared to T~8000K one day previous, as reported by Malesani et al (GCN 21577) and Cowperthwaite et al (GCN 21578). The blackbody radius (~8e14 cm) indicates an average velocity ~0.1c, suggesting the expansion has now slowed compared to those earlier estimates (0.2-0.3c). We note the possibility of weak, broad bumps at ~5000 and ~6000 Ang in our quick extractions. ======================= Matt Nicholl Postdoctoral Research Fellow Harvard-Smithsonian Center for Astrophysics mattnicholl.net ======================= //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21586 SUBJECT: LIGO/Virgo G298048: HSC observations of the OT candidate of G298048 DATE: 17/08/19 06:52:33 GMT FROM: Nozomu Tominaga at Konan U Yoshida, M., Tanaka, M., Terai, T., Nakata, F., Tajitsu, A., Fujiyoshi, T. (NAOJ), Utsumi, Y., Kawabata K. S. (Hiroshima U.), Tominaga, N. (Konan U.), Motohara, K., Ohsawa, R., Morokuma, T. (Univ. of Tokyo), Kawai, N. (Tokyo Tech.), and Asakura, Y. (Nagoya Univ.) on behalf of the J-GEM collaboration We performed follow-up observations for the gravitational wave event G298048 with Hyper Suprime-Cam attached to the Subaru telescope from 5:20 to 6:00 on August 19 2017 UT. We surveyed the same sky area as our previous observation (GCN 21549) with HSC-z band filter. SSS17a, which is the most promising candidate of the optical counterpart of G298048 (GCN 21529), was still bright. The rough estimation of the z-band magnitude of the object was ~17.7 (AB). Further analysis is ongoing. The sky fields observed by this survey are listed below: ID Time RA DEC Exp Filter ----------------------------------------------------------- 28 2017-08-19T05:21:42 13h10m14.4s -23d19m20.0s 2.0s HSC-z 04 2017-08-19T05:22:21 13h07m25.6s -26d36m51.9s 10.0s HSC-z 05 2017-08-19T05:23:02 13h10m14.3s -27d17m02.1s 10.0s HSC-z 06 2017-08-19T05:23:46 13h13m03.0s -27d57m27.1s 10.0s HSC-z 07 2017-08-19T05:24:28 13h15m51.8s -28d38m07.2s 10.0s HSC-z 08 2017-08-19T05:25:11 13h18m40.5s -29d19m03.0s 10.0s HSC-z 09 2017-08-19T05:25:57 13h21m29.2s -30d00m15.5s 10.0s HSC-z 28 2017-08-19T05:26:44 13h10m14.4s -23d19m20.0s 30.0s HSC-z 10 2017-08-19T05:27:44 13h04m36.9s -24d37m43.0s 30.0s HSC-z 11 2017-08-19T05:28:45 13h07m25.6s -25d17m13.0s 30.0s HSC-z 12 2017-08-19T05:29:47 13h10m14.4s -25d56m55.7s 30.0s HSC-z 13 2017-08-19T05:30:48 13h13m03.1s -26d36m52.0s 30.0s HSC-z 28 2017-08-19T05:31:49 13h10m14.4s -23d19m20.0s 30.0s HSC-z 14 2017-08-19T05:32:51 13h01m48.2s -22d40m26.0s 30.0s HSC-z 15 2017-08-19T05:33:54 13h15m51.8s -27d17m02.0s 30.0s HSC-z 16 2017-08-19T05:34:55 13h18m40.5s -27d57m27.0s 30.0s HSC-z 17 2017-08-19T05:35:59 13h04m36.9s -23d19m20.1s 30.0s HSC-z 18 2017-08-19T05:37:00 13h07m25.7s -23d58m25.6s 30.0s HSC-z 19 2017-08-19T05:38:02 12h58m59.5s -20d44m48.0s 30.0s HSC-z 20 2017-08-19T05:39:03 13h10m14.4s -24d37m43.1s 30.0s HSC-z 22 2017-08-19T05:40:05 13h13m03.1s -25d17m12.9s 30.0s HSC-z 23 2017-08-19T05:41:06 13h15m51.9s -25d56m55.6s 30.0s HSC-z 24 2017-08-19T05:42:15 12h56m10.8s -18d50m37.3s 30.0s HSC-z 25 2017-08-19T05:43:15 13h04m37.0s -22d01m43.1s 30.0s HSC-z 26 2017-08-19T05:44:15 13h07m25.7s -22d40m26.2s 30.0s HSC-z 29 2017-08-19T05:45:16 13h01m48.3s -20d06m35.2s 30.0s HSC-z 28 2017-08-19T05:46:17 13h10m14.4s -23d19m20.1s 30.0s HSC-z 28 2017-08-19T05:47:17 13h10m14.4s -23d19m20.1s 120.0s HSC-z 28 2017-08-19T05:49:48 13h10m14.4s -23d19m20.0s 120.0s HSC-z 28 2017-08-19T05:52:20 13h10m17.5s -23d18m06.5s 60.0s HSC-z ----------------------------------------------------------- //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21587 SUBJECT: LIGO/Virgo G298048: MASTER photometry of the SSS17a in NGC 4993 DATE: 17/08/19 08:10:30 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs V.M.Lipunov, E. Gorbovskoy, V.G.Kornilov, N.Tyurina, V.Shumkov, D.Kuvshinov, P.Balanutsa, O.Gress, A.Kuznetsov, M.I.Panchenko, A.V.Krylov, I.Gorbunov Lomonosov Moscow State University, Sternberg Astronomical Institute D.Buckley, S.Potter, M.Kotze, South African Astronomical Observatory R.Podesta, C.Lopez, F.Podesta Observatorio Astronomico Felix Aguilar (OAFA) , National University of San Juan, Argentina H.Levato, C.Saffe Instituto de Ciencias Astronomicas,de la Tierra y del Espacio (ICATE), San Juan, Argentina N.M. Budnev, O. Gress, K. Ivanov, S.Yazev Irkutsk State University V.Yurkov, Yu.Sergienko, A.Gabovich Blagoveschensk Educational State University, Blagoveschensk R. Rebolo, M. Serra-Ricart, G. Israelian, N.Lodiu The Instituto de Astrofisica de Canarias A. Tlatov, V.Sennik Kislovodsk Solar Station of the Pulkovo Observatory As we reported in LVC GCN 21546 MASTER-OAFA have imaged the BAYESTAR localization map of LIGO/Virgo G298048 (GCN 21513). MASTER-SAAO have new images of NGC 4993 galaxy starting 2017-08-18 17:06:55 UT in B, R and unfiletred with magnitude limit 19.8 (Lipunov et al., LVC GCN 21570). We see object in B, R and unfiltered images detected by Coulter et al. (LVC GCN 21529), Allam et al. (LVC GCN 21530), Yang et al. (LVC GCN 21531), Melandri et al. (LVC GCN 21532), Lipunov et al., (LVC GCN 21546). B = 18.5 +- 0.2 R = 17.5 +- 0.2 W = 18.0 +- 0.2 The unfiltered magnitude not changed with respect to first observations (Lipunov et al., LVC GCN 21546) This message can be citted. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21588 SUBJECT: LIGO/Virgo G298048: VLBA observations of the possible counterpart SSS17a in NGC 4993 DATE: 17/08/19 09:36:26 GMT FROM: Igor Andreoni at Swinburne U of Tech A. Deller (Swinburne/OzGrav), M. Bailes (Swinburne/OzGrav), I. Andreoni (Swinburne/OzGrav/AAO), K. Bannister (CSIRO), J. Cooke (Swinburne/OzGrav), D. Dobie (University of Sydney), D. Kaplan (UWM) C. Lynch (University of Sydney), T. Murphy (University of Sydney), on behalf of a joint effort between OzGrav and the VAST collaboration. We are observing the optical transient SSS17a (Coulter et al. - GCN 21529, Allam et al. - GCN 21530, Yang et al.- GCN 21531, Melandri et al. - GCN 21532) and its host galaxy NGC 4993 with the Very Long Baseline Array. We are observing at a central frequency of 8.7 GHz with a bandwidth of 256 MHz. The first observation took place from 2017-08-17 19:58UT to 2017-08-18 01:34UT. Analysis of the data will take place after correlation, in 7-10 days. Two subsequent epochs are planned in the coming three days. We thank the Long Baseline Observatory staff for facilitating these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21589 SUBJECT: LIGO/Virgo G298048: Further VLA Observations DATE: 17/08/19 09:51:33 GMT FROM: Kate Alexander at Harvard U K.D. Alexander (Harvard), W. Fong (Northwestern), and E. Berger (Harvard) report on behalf of a larger collaboration: We analyzed observations taken with the Very Large Array beginning on 2017 Aug 18 at 22:04:57 UT (1.39 d after the Fermi trigger time; Blackburn et al., LVC GCN 21506). In two hours of observations at a mean frequency of 10.0 GHz, we detect the source reported in our previous VLA observations (Alexander et al., LVC GCN 21545; 21548) and in ATCA observations (Bannister et al., LVC GCN 21559) at a similar flux level. We measure an improved position of: RA = 13:09:47.704 Dec =-23:23:02.45 with an uncertainty of 0.1” in each coordinate. We note that the beam size in our images is 3.1” by 1.4”, significantly smaller than our previous VLA observations. The lack of variability over a 19.9 hr period along with full spatial coincidence with NGC 4993 indicates that this radio emission is originating from the host galaxy. We further note that there is no detected emission at the position of the optical transient (Coulter et al., LVC GCN 21529) down to a 3-sigma limit of 17 microJy. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21590 SUBJECT: LIGO/Virgo G298048: Further Pan-STARRS izy photometry confirms rapid fading of SSS17a/DLT17ck in i and z bands DATE: 17/08/19 10:14:53 GMT FROM: S. J. Smartt at Queens U Belfast K. C. Chambers (IfA), S. J. Smartt, (QUB), M. E. Huber (IfA), K. W. Smith (QUB), D. R. Young, M. Coughlin (Harvard), T.-W. Chen (MPE), J. Bulger, L. Denneau, H. Flewelling, A. Heinze, E. Kankare (QUB), T. Lowe, E. A. Magnier (IfA), A. Rest (STScI), B. Stalder (IfA), A. S. B. Schultz, C. W. Stubbs (Harvard) J. Tonry, C. Waters, R. J. Wainscoat, H. Weiland, M. Willman (IfA), D. E. Wright (QUB) We report continued Pan-STARRS imaging of the transient SSS17a/DLT17ck in NGC4339 in filters i, z and y (see Chambers et al. GCN 21553 for more details of filters, photometry, methods etc). Our reference stack and calibrations provide rapid reliable photometry with the host removed and we will continue to post updates while it is visible from Hawaii. A series of short exposures to avoid sky saturation in twilight in each of i, z, and y provide average nightly magnitudes (AB) of MJD i err 57983.23 17.24 0.06 57984.24 17.91 0.05 MJD z err 57983.23 17.26 0.06 57984.24 17.80 0.05 MJD y err 57983.23 17.38 0.10 57984.24 17.59 0.07 This confirms the fading seen in the DECam images (Nicholl et al. GCN 21580), and is consistent with the other reports of fading (e.g. Yoshida et al. GCN 21586, Yang et al. 21579, Arcavi et al. 21581). The fading in i-band and bluer bands is clearly more pronounced than in y-band and distinct from the rising NIR (Wiseman et al GCN 21584). This rate of fading is quantitatively similar to that of the kilonova or merging NS models (Kasen et al. 2015, Barnes & Kasen 2013, Tanaka et al. 2014). And is uncommon for the populations of known nearby transients. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21591 SUBJECT: LIGO/Virgo G298048: NOT near-infrared observations of SSS17a DATE: 17/08/19 12:00:05 GMT FROM: Daniele Malesani at DARK/NBI D. Malesani (DARK/NBI), E. Pian (INAF-IASF Bo), J. Hjorth (DARK/NBI), D. J. Watson (DARK/NBI), L. Amati (INAF-IASF Bo), L. A. Antonelli, (INAF-OAR), S. Ascenzi (INAF-OAR), S. Benetti (INAF-OAPD), M.T. Botticella (INAF-OAC), M. Branchesi (GSSI), S. Campana (INAF-OAB), E. Cappellaro (INAF-OAPD), S. Covino (INAF-OAB), P. D'Avanzo (INAF-OAB), V. D'Elia (INAF-ASDC), D. Fugazza (INAF-OAB), F. Getman (INAF-OAC), A. Grado (INAF-OAC), G. Greco (Urbino University/INFN Firenze), L. Limatola (INAF-OAC), M. Lisi (INAF-OAR), A. Melandri (INAF-OAB), L. Nicastro (INAF-IASF Bo), E. Palazzi (INAF-IAFS Bo), S. Piranomonte (INAF-OAR), L. Pulone (INAF-OAR), A. Rossi (INAF-IASF Bo), P. Schipani (INAF-OAC), G. Stratta (Urbino University/INFN Firenze), G. Tagliaferri (INAF-OAB), V. Testa (INAF-OAR), L. Tomasella (INAF-OAPD), S. Yang (INAF-OAPD), E. Brocato (INAF-OAR) on behalf of GRavitational Wave Inaf TeAm report: We observed object SSS17a (Coulter et al., GCN 21529; Allam et al., GCN 21530; Yang et al., GCN 21531) possibly associated with the LIGO/Virgo event G298048 (GCN 21509), using the Nordic Optical Telescope located in La Palma (Canary Islands, Spain). Observations were carried out around Aug 18.85 UT (1.32 days after the GW event), and consisted of 9 min exposure in each of the J and K filters. Conditions were difficult due to the large airmass (4.0 to 5.5) and the still bright twilight sky, which led to an unusually elongated PSF due to imperfect focusing. SSS17a is well visible in the J image and faintly detected in K. Based on the 2MASS catalog, we provide preliminary magnitudes J = 16.23 +- 0.11 and K = 15.88 +- 0.25 (both Vega). We note that an extra error may arise from the non-circular PSF and the uneven background around the nearby NGC 4993. Our fluxes are earlier and fainter than the GROND measurements (Wiseman et al., GCN 21584), confirming the brightening of SSS17a at NIR wavelengths and the overall cooling trend noted by several authors (e.g., Cenko et al., GCN 21572; Lyman et al., GCN 21582; Wiseman et al., GCN 21584). We acknowledge excellent support of the NOT visiting observer, Auni Somero, in carrying out this difficult observation. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21592 SUBJECT: LIGO/Virgo G298048: GRAWITA VLT/X-shooter observations DATE: 17/08/19 12:16:37 GMT FROM: Andrea Melandri at INAF-OAB E. Pian (INAF-IASF Bo), V. D'Elia (INAF-ASDC), S. Piranomonte (INAF-OAR), M. Branchesi (GSSI), S. Campana (INAF-OAB), E. Cappellaro (INAF-OAPD), S. Covino (INAF-OAB), P. D'Avanzo (INAF-OAB), A. Grado (INAF-OAC), G. Greco (Urbino University/INFN Firenze), A. Melandri (INAF-OAB), E. Palazzi (INAF-IASF Bo), G. Stratta (Urbino University/INFN Firenze), L . Tomasella (INAF-OAPD), L. Amati (INAF-IASF Bo), L. A. Antonelli, (INAF-OAR), S. Ascenzi (INAF-OAR), S. Benetti (INAF-OAPD), M.T. Botticella (INAF-OAC), D. Fugazza, F. Getman (INAF-OAC), L. Limatola (INAF-OAC), M. Lisi (INAF-OAR), L. Nicastro (INAF-IASF Bo), L. Pulone (INAF-OAR), A. Rossi (INAF-IASF Bo), P. Schipani (INAF-OAC), G. Tagliaferri (INAF-OAB), V. Testa (INAF-OAR), S. Yang (INAF-OAPD), L. Sbordone (ESO) and E. Brocato (INAF-OAR) on behalf of GRavitational Wave Inaf TeAm and the team of the ESO VLT program 099.D-0382(A) report: We observed object SSS17a (Coulter et al., GCN 21529; Allam et al., GCN 21530; Yang et al., GCN 21531, Melandri et al., GCN 21532) possibly associated with the LIGO/Virgo event G298048 (GCN 21509), with the ESO Very Large Telescope UT 2 (Kueyen) equipped with the X-shooter spectrograph, covering the wavelength range 3000-25000 AA. Observations started at 23:16 UT on 2017-08-18, during the twilight, roughly 1.5 days after the burst and consisted of 4 exposures of 600 s each. The transient is bright, well detected in the acquisition image, and clearly visible in all the spectral range. After a preliminary reduction the continuum appears to be similar to that predicted by kilonova models (Tanaka & Hotokezaka 2013, ApJ, 775, 113; Kasen et al. 2015, MNRAS, 450, 1777, Rosswog et al. 2016, arxiv1611.09822). We do not detect any obvious emission lines throughout the spectrum. Further X-shooter observations are planned. We acknowledge excellent support from the ESO observing staff in Paranal, in particular N. Jimenez and S. Brillant. [GCN OPS NOTE(20aug17): Per author's request, (a) the 1st & 2nd authors exchanged order, (b) a couple other changes in the rest of the author list, and (c) LS was removed the 4th paragraph.] [GCN OPS NOTE(21aug17): Per author's request (D'Elia), G. Greco was added to the author list.] [GCN OPS NOTE(16sep17): Per author's request (Pian), (a) the phrase "and tentative redshift of SSS17a" was removed from the Subject-line, and (b) the last 4 sentences in the second paragraph were removed.] //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21594 SUBJECT: LIGO/Virgo G298048: VLT linear polarimetry DATE: 17/08/19 14:13:15 GMT FROM: Klaas Wiersema at U of Leceister K. Wiersema (University of Leicester), S. Covino (INAF-OAB), A. Melandri (INAF-OAB) and E. Palazzi (INAF-IAFS Bo) report on behalf of a large collaboration: We obtained optical linear polarimetry measurements of object SSS17a (Coulter et al., GCN 21529; Allam et al., GCN 21530; Yang et al., GCN 21531, Melandri et al., GCN 21532) possibly associated with the LIGO/Virgo event G298048 (GCN 21509). We used the ESO Very Large Telescope UT1 (Antu) equipped with the FORS2 instrument. Observations started on 23:09 UT on 18 August 2017, i.e. during twilight, and continued until the source reached airmass 2. FORS2 uses a Wollaston element and a rotating halfwave plate to perform imaging polarimetry; additionally we used the FORS2 R_special filter (similar to R) . We obtained a large series of imaging polarimetry datasets, each consisting of 4 angles of the wave plate, using exposure times of 60 seconds for each exposure; the transient is bright in our data. In a preliminary analysis of a subset of our data, we find no evidence of optical linear polarisation, with a preliminary upper limit on the linear polarisation of P_linear < 1%. We expect this value to change somewhat through a more thorough analysis in the future, e.g. using more accurate models to correct for the host galaxy emission and rapidly varying twilight contribution. Our polarisation limit is a first for a kilonova candidate, and indicates a relatively smooth emission region, with no evidence of significant asymmetry at the time of observations. Similarly, this limit may indicate that there is no large contribution of non-thermal emission in the observed wavelength at the time of observations. We acknowledge excellent support from the ESO staff, J. M. Corral-Santana and S. Brilliant, and in particular the visiting observer, M. Lendl, who so kindly gave up some of their observing time. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21595 SUBJECT: LIGO/Virgo G298048: Subaru HSC z-band photometry confirms the fading nature of SSS17a DATE: 17/08/19 14:46:41 GMT FROM: Nozomu Tominaga at Konan U Tominaga, N. (Konan Univ.), Yoshida, M., Tanaka, M., Terai, T., Nakata, F., Furusawa, H., Koshida, S. (NAOJ), Utsumi, Y., Kawabata K. S. (Hiroshima Univ.), Motohara, K., Ohsawa, R., Morokuma, T., Yasuda, N. (Univ. of Tokyo), Kawai, N. (Tokyo Tech), and Asakura, Y. (Nagoya Univ.) on behalf of the J-GEM collaboration We performed z-band imaging observations for the gravitational wave event G298048 (GCN 21505; 21509; 21513) with Hyper Suprime-Cam attached to the Subaru telescope on August 19 2017 UT (Yoshida et al. GCN 21586). We made photometric calibration with Pan-STARRS1 catalog (Chambers et al. 2016) using HSC pipeline (Bosch et al. 2017) and obtained psf magnitude of SSS17a (Coulter et al. 2017; GCN 21529) as z = 17.8 (AB) (2017-08-19 05:26--05:52UT), which is 0.5 mag fainter than the psf magnitude obtained with Subaru/HSC on August 18 UT (Yoshida et al. GCN 21561). The fading nature of SSS17a in the z-band is consistent with the reports in Nicholl et al. (GCN 21580) and Chambers et al. (GCN 21590). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21596 SUBJECT: LIGO/Virgo G298048: further REM optical/NIR observations of candidate in NGC 4993 DATE: 17/08/19 16:38:19 GMT FROM: Andrea Melandri at INAF-OAB A. Melandri, P. D'Avanzo, S. Campana, S. Covino (INAF-OAB), G. Greco (Urbino University/INFN Firenze), M. Branchesi (GSSI), D. Fugazza (INAF-OAB), L. Amati (INAF-IASF Bo), L. A. Antonelli, (INAF-OAR), S. Ascenzi (INAF-OAR), M.T. Botticella (INAF-OAC), E. Cappellaro (INAF-OAPD), V. D'Elia (INAF-ASDC), F. Getman (INAF-OAC), A. Grado (INAF-OAC), L. Limatola (INAF-OAC), M. Lisi (INAF-OAR), L. Nicastro (INAF-IASF Bo), E. Palazzi (INAF-IAFS Bo), E. Pian (SNS-Pisa), S. Piranomonte (INAF-OAR), L. Pulone (INAF-OAR), A. Rossi (INAF-IASF Bo), G. Stratta (Urbino University/INFN Firenze), G. Tagliaferri (INAF-OAB), V. Testa (INAF-OAR), L . Tomasella (INAF-OAPD), S. Yang (INAF-OAPD), E. Brocato (INAF-OAR) on behalf of GRavitational Wave Inaf TeAm report: We continued the optical/NIR follow-up monitoring of the LIGO/Virgo GW trigger G298048 (LVC GCN Circ. 21509, 21513) with the 60-cm robotic telescope REM located at the La Silla Observatory (Chile) by performing targeted observations of catalogued galaxies in the LVC skymap. The observations were carried out from 23:31 UT on 2017 Aug 18 to 01:18 UT on on 2017 Aug 19, simultaneously in the g, r, i, z, J, H and K bands. We clearly detect in all bands the optical source reported by Coulter et al. (LVC GCN 21529, 21567), Allam et al. (LVC GCN 21530), Yang et al. (LVC GCN 21531, 21579), Melandri et al. (LVC GCN 21532), Arcavi et al. (LVC GCN 21538, 21581), Nicholl et al. (LVC GCN 21541, 21580), Tanvir & Levan (LVC GCN 21544), Evans et al. (LVC GCN 21550), Simon et al.(LVC GCN 21551), Singer et al. (LVC GCN 21552), Chambers et al. (LVC GCN 21553, 21590), wolf et al. (LVC GCN 21560), Yoshida et al. (LVC GCN 21561, 21586), Kilpatrick et al. (LVC GCN 21583) and Wieseman et al. (LVC GCN 21584). With respect to our previous epoch (Melandri et al. LVC GCN 21532), preliminary analysis shows that the source is significantly fainter in the g-band and displays no variation in the r-band. Analysis and calibration is ongoing and further observations are planned. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21597 SUBJECT: LIGO/Virgo G298048: KMTNet and other optical follow-up observations DATE: 17/08/19 16:55:08 GMT FROM: Myungshin Im at Seoul National U M. Im, C. Choi, J. Kim, H. M. Lee (SNU), S.-L. Kim, C.-W. Lee (KASI) on behalf of the KU collaboration We continued to observe the optical counterpart candidate of LIGO/Virgo G298048 (LVC GCNs 210505, 21509, 21513), SSS17a (Coutler et al. LVC GCN 21529), using the KMTNet 1.5m telescopes and other small telescopes. KMTNet is an observing system made of three 1.5m telescopes at the Siding Spring Observatory (SSO), the South African Astronomical Observatory (SAAO), and the Cerro-Tololo Inter-American Observatory (CTIO). BVRI images were taken at each KMTNet site in 2017-08-18 and 08-19 UT. Preliminary magnitudes in R-band shows continued dimming of SSS17a (e.g., Im et al. LVC GCN 21566), and more interestingly, SSR17a seems to be fading faster in the last epoch data taken at SSO (see also Melandri et al. LVC GCN 21596). UT R (mag) Site 2017-08-18.71 17.4 +- 0.1 SAAO 2017-08-18.98 17.7 +- 0.1 CTIO 2017-08-19.35 18.4 +- 0.2 SSO The observation using small telescopes at SSO was carried out too (see Im et al. LVC GCN 21563), and the images taken with these telescopes also suggest faster dimming. The observations using the KMTNet telescopes and the small telescopes are ongoing. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21598 SUBJECT: LIGO/VIRGO G298048: INAF VST-ESO PARANAL observations DATE: 17/08/19 17:37:19 GMT FROM: Aniello Grado at INAF-OAC A. Grado (INAF-OAC), E. Cappellaro (INAF-OAPD), G. Greco (Urbino University/INFN Firenze), M. Branchesi (GSSI), S. Covino (INAF-OAB), P. D'Avanzo (INAF-OAB), F. Getman (INAF-OAC), A. Melandri (INAF-OAB), L. Amati (INAF-IASF Bo), L. A. Antonelli, (INAF-OAR), S. Ascenzi (INAF-OAR), S. Benetti (INAF-OAPD), M.T. Botticella (INAF-OAC), S. Campana (INAF-OAB), V. D'Elia (INAF-ASDC), D. Fugazza, L. Limatola (INAF-OAC), M. Lisi (INAF-OAR), L. Nicastro (INAF-IASF Bo), E. Palazzi (INAF-IAFS Bo), E. Pian (SNS-Pisa), S. Piranomonte (INAF-OAR), L. Pulone (INAF-OAR), A. Rossi (INAF-IASF Bo), P. Schipani (INAF-OAC), G. Stratta (Urbino University/INFN Firenze), G. Tagliaferri (INAF-OAB), V. Testa (INAF-OAR), L . Tomasella (INAF-OAPD), S. Yang (INAF-OAPD), E. Brocato (INAF-OAR) on behalf of GRavitational Wave Inaf TeAm report: Observations of 9 square degrees of the skymap of the Advanced LIGO and Virgo trigger G298048 (LVC GCN Circ. 21509, 21513) were performed with the VLT Survey Telescope (VST - Proposal ID ESO 099.D-0191) at ESO-Paranal equipped with OMEGACAM (FOV=1 square degree). The observation of the 3 x 3 square degrees region is centered on the following coordinates: RA, Dec (ICRSd): 194.30420 -17.85690 The VST pointings was generated using the GWsky script ( https://github.com/ggreco77/GWsky). Starting from the high probability region of the skymap, the sequence was defined to maximize the contained localization probability. The images were taken in the r_SDSS filter with an exposure of 80s (split in two dithered exposures of 40 s each). The observations started at 2017-08-17T 23:44:50.964 UTC and finished at 2017-08-18T 00:08:46.388. Automatic data reduction with the VSTTube pipeline (Grado et al. 2012 Mem.SAIt 19, 362 ) was completed. The image analysis is ongoing. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21599 SUBJECT: LIGO/Virgo G298048: La Silla - QUEST archival non-detections of of LIGO EM counterpart SSS17a DATE: 17/08/19 18:04:05 GMT FROM: David Rabinowitz at Yale D. Rabinowitz and C. Baltay (Yale) report: The La Silla - QUEST supernova survey (conducted with the 160-Megapixel QUEST camera on the ESO 1.0m Schmidt at La Silla, Chile from 2010 to 2016) covered the location of SSS17a (Coulter et al. LVC GCN 21529) with 345 exposures to depth ~R=19 in the years 2013 to 2016 (~100 exposures per year). Visual inspection of these images at the location of SSS17a shows no point source to limit ~R=18. [GCN OPS NOTE(18aug17): Per submitter's and author's request, the submitter was changed from Singer to Rabinowitz to work around a momentary problem.] //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21603 SUBJECT: LIGO/Virgo G298048: GMRT Follow-up of SSS17a DATE: 17/08/19 21:18:21 GMT FROM: Mansi M. Kasliwal at Caltech K. De (Caltech), M. M. Kasliwal (Caltech), V. Bhalerao (IIT-B), P. Chandra (NCRA), A. Corsi (TTU) report on behalf of the GROWTH (Global Relay of Observatories Watching Transients Happen) collaboration We observed SSS17a (GCN 21529) with the Giant Meterwave Radio Telescope in India at 610 MHz on UT 2017-08-18 11:00. We do not detect any emission at this location. Multi-band multi-epoch follow-up is underway. We thank the GMRT staff for rapidly scheduling these observations. The GMRT is run by the National Centre for Radio Astrophysics of the Tata Institute of Fundamental Research. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21606 SUBJECT: LIGO/Virgo G298048: Continued observation for DLT17ck DATE: 17/08/19 23:31:25 GMT FROM: Stefano Valenti at UC Davis Stefano Valenti (UC Davis), Sheng Yang (INAF-OAPd, UC Davis), David Sand (UA), Leonardo Tartaglia (UA, UC Davis), Enrico Cappellaro(INAF-OAPd), Dan Reichart, Josh Haislip, Vladimir Kouprianov (UNC) report on behalf of the Gravitational Wave Follow-Up by DLT40. We continued to monitor DLT17ck/SSS17a (GCN 21529;GCN21530; GCN21531), the electromagnetic counterpart candidate of the LIGO/Virgo GW G298048 (GCN21509). Following the optical observations reported for DLT17ck/SSS17a (GCN21579; GCN21531; GCN21567; GCN21541; GCN21590; GCN21553; GCN21560; GCN21584; GCN21580; GCN21583; GCN21590; GCN21595; GCN21597), here we report that DLT17ck/SSS17a is continuing fading. Using data from the PROMPT 5 0.41m telescope located at CTIO, DLT40 observation began at 2017 August 19.99 UT and shows the source at magnitude r = 18.96 ± 0.10 mag. We also observed DLT17ck in i and z, for which analysis is under way. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21608 SUBJECT: LIGO/Virgo G298048: GROND observations of candidate optical counterpart DATE: 17/08/20 04:49:21 GMT FROM: Ting-Wan Chen at PESSTO T.-W. Chen, P. Wiseman, J. Greiner, and P. Schady (all MPE Garching) report on behalf of the GROND team: We observed the field of the transient source SSS17a in NCG 4993 (RA = 13:09:48.09 DEC = -23:22:53.35, discovered by Coulter et al. GCN #21529), possibly associated with LIGO/Virgo trigger G298048, simultaneously in g'r'i'z'JHK with GROND (Greiner et al. 2008, PASP 120, 405) mounted at the 2.2 m MPG telescope at ESO La Silla Observatory (Chile). Observations started at 23:15 UT on August 19th 2017. They were performed at an average seeing of 1.8" and at an average airmass of 1.4. We detected a single point source at the location of the transient, although the strong host contribution hinders photometric accuracy. Based on the first 11.7 min of total exposures in g'r'i'z' and 13.2 min in JHK, we estimate preliminary magnitudes using aperture photometry (all in AB system) of g' = 19.8 +/- 0.2 mag, r' = 18.1 +/- 0.1 mag, i' = 18.0 +/- 0.1 mag, z' = 16.8 +/- 0.1 mag, J = 16.4 +/- 0.2 mag, H = 16.6 +/- 0.2 mag, and K = 16.6 +/- 0.2 mag. We confirm that the transient significantly declines in optical brightness (Yoshida et al. GCN #21586, Chambers et al. GCN #21590, Tominaga et al. GCN #21595, Melandri et al. GCN #21596, Im et al. GCN #21597, Valenti et al. GCN #21606), but the transient keeps flat in z'JHK-band brightness for 1 day compared to our previous report (Wiseman et al. GCN #21584). Given magnitudes are calibrated against Pan-STARRS1 field stars as well as 2MASS field stars and are not corrected for the expected Galactic foreground extinction corresponding to a reddening of E_(B-V)= 0.1 mag in the direction of the candidate (Schlafly & Finkbeiner 2011). We acknowledge the excellent help in obtaining these data from Angela Hempel on La Silla. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21609 SUBJECT: LIGO/Virgo G298048: Etelman Observatory observation of the potential LIGO EM counterpart SSS17a DATE: 17/08/20 05:27:49 GMT FROM: Bruce Gendre at U of Virgin Islands B. Gendre (UVI), A. Cucchiara (UVI), D. Morris (UVI), N. Orange (OrangeWave Innovative Science, LLC), D. Drost (UVI), T. Giblin (USAF Academy), J. Hakkila (College of Charleston), A. Klotz (IRAP), J. Neff (NSF), D. Smith (UVI), J. Staff (UVI), P. Thierry (Auragne Observatory), R. Watlington (UVI), on behalf of the FIGARO collaboration report: We observed the field of SSS17a (Coulter et al., GCN 21529; Allam et al., GCN 21530; Yang et al., GCN 21531), the potential counterpart of the LIGO/Virgo event G298048 (GCN 21509), with the 0.5m Virgin Island Robotic Telescope (VIRT) on August the 19th, starting at 23:19 UT. We performed a series of exposures in the R and Clear filters, with an elevation decreasing from 40 degrees. The weather conditions were good, with a mean seeing of 2-3 arcsec. We detect an excess at the position of the potential counterpart in C filter at 23:54 UT. Strong contamination from the nearby galaxy prevents a precise brightness estimate without galaxy substraction. Further analysis is in progress. The VIRT is still in its commissioning phase. This message can be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21610 SUBJECT: LIGO/VIRGO G298048: SALT optical spectra of the candidate optical/NIR counterpart of the gravitational wave G298048 in NGC4993. DATE: 17/08/20 06:14:37 GMT FROM: Stephen Potter at SAAO M. Shara (AMNH), T. Williams (SAAO), P. Vaisanen (SAAO/SALT), S. Potter (SAAO), E. Romero Colmenero (SAAO/SALT), S. Crawford (SAAO), D. Buckley (SAAO), J Cooke (Swinburne), Igor Andreoni (Swinburne), Tyler Pritchard (Swinburne), Jirong Mao (YNAO) Spectra of an unresolved source at coordinates RA=197.4504, DEC=-23.3815 near the galaxy NGC 4993, obtained with the Robert Stobie Spectrograph on the Southern African Large Telescope at UT 17:07:19.703 on 18 August 2017 and at UT 16:58:32.764 on 19 August 2017 during early twilight. The spectra extends between 3600-8000 Angstroms with a resolution of ~300. The spectra is heavily blended with the host galaxy. After subtraction of the host galaxy spectra from the 18 August, the source shows a spectra increasing in flux from 8000 A to 5000 A, which then decreases in flux after 4500 A. The spectra from the 19 August 2017 was taken early twilight and too noisy to say anything definitive. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21612 SUBJECT: LIGO/Virgo G298048: Possible X-ray detection with Swift DATE: 17/08/20 08:42:40 GMT FROM: Phil Evans at U of Leicester P.A. Evans (U. Leicester), J.A. Kennea (PSU), S.B. Cenko (NASA/GSFC), B. Sbarufatti (INAF-OAB/PSU), S. Campana (INAF-OAB), E. Troja (NASA/GSFC/UMCP) S.D. Barthelmy (NASA/GSFC), A.P. Beardmore (U. Leicester), A.A. Breeveld (UCL-MSSL), D.N. Burrows (PSU), , G. Cusumano (INAF-IASF PA), A. D'Ai (INAF-IASFPA), P. D'Avanzo (INAF-OAB), V.D'Elia(ASDC), S.W.K. Emery (UCL-MSSL), P. Giommi (ASI), C. Gronwall (PSU), H.A. Krimm (CRESST/GSFC/USRA), N.P.M. Kuin (UCL-MSSL), A.Y. Lien (GSFC/UMBC), F.E. Marshall (NASA/GSFC), A. Melandri (INAF-OAB), J.A. Nousek (PSU), S.R. Oates (U. Warwick), P.T. O'Brien (U. Leicester), J.P. Osborne (U. Leicester), C. Pagani (U. Leicester), K.L. Page (U.Leicester), D.M. Palmer (LANL), M. Perri (ASDC), J.L. Racusin (NASA/GSFC), M.H. Siegel (PSU), G. Tagliaferri (INAF-OAB), A. Tohuvavohu (PSU) report on behalf of the Swift team: Swift has continued to monitor the position of the likely EM counterpart to the LVC trigger G298048. We have now collected a total of 19.3 ks at the position of the optical source first reported by Coulter et al. (LVC GCN 21529). In the summed data a faint X-ray source is detected at a position of (RA,Dec)=194.45112, -23.3845 degrees which is equivalent to: RA (J2000.0) = 13h 09m 48.27s Dec (J2000.0) = -23d 23’ 04.3” with an uncertainty of 6.4 arcsec (radius, 90% confidence). This source is 11.3 arcsec from the position reported by Coulter et al. The mean count rate is 6.5 (+2.8,-2.2) e-4 ct/sec which corresponds to a 0.3-10 keV flux of 2.6 (+1.1, -0.9) e-14 erg/cm^2/s. Assuming a distance of 42.5 Mpc (D’Elia et al., LVC Circ. 21592) this corresponds to a luminosity of 5.6 (+2.4, -1.9)e39 erg/s. In the data binned per Swift pointing, the peak detection is at ~twice this level. At the current time we do not have sufficient statistics to confirm whether the object is variable. We also note that, given the probable radio emission from the host (Alexander, Fong & Berger, LVC Circ. 21548) the host may be a weak AGN, at the current time we cannot rule out the possibility that the X-rays come from the host galaxy rather than the optical afterglow. Further observations are planned. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21613 SUBJECT: LIGO/Virgo G298048: Continued VLA observations DATE: 17/08/20 09:17:57 GMT FROM: Alessandra Corsi at Texas Tech U. A. Corsi (TTU) and M.M. Kasliwal (Caltech) report on behalf of a larger collaboration: We analyzed a further Karl G. Jansky VLA observation of the field of SSS17a, the possible counterpart of G298048 in NGC 4993 identified by Coulter et al. (LVC GCN 21529). The observation started on 2017-Aug-19 22:01:48 UT, ended on 2017-Aug-20 00:01:24 UT, and was conducted with the VLA in its C configuration in C-X-Ku-bands. At a central frequency of ~9.7 GHz, our preliminary analysis does not show any significant emission at the location of the optical candidate SSS17a down to a 3-sigma limit of about 18 uJy. We detect the host at a flux level consistent with what measured by Alexander et al. (LVC GCN 21545). Analysis of the data collected in other bands is on-going. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21614 SUBJECT: LIGO/Virgo G298048: VLA observation at 6 GHz DATE: 17/08/20 10:26:01 GMT FROM: Alessandra Corsi at Texas Tech U. A. Corsi (TTU) and M.M. Kasliwal (Caltech) report on behalf of a larger collaboration: We analyzed the Karl G. Jansky VLA observation of the field of the possible optical counterpart SSS17a (Coulter et al. LVC GCN 21529) that started on 2017-Aug-19 22:01:48 UT (Corsi et al. LVC GCN 21613). At a central frequency of ~6 GHz, our preliminary analysis does not show any significant emission at the location of the optical candidate (RA= 13:09:48.089, Dec= -23:22:53.35, Coulter et al. LVC GCN 21529) down to a 3-sigma limit of ~22 uJy. We detect the host emission (RA = 13:09:47.704, Dec =-23:23:02.45; Alexander et al. LVC GCN 21589) at a flux level of ~0.3 mJy at 6 GHz. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21617 SUBJECT: LIGO/Virgo G298048: Pan-STARRS izy photometry monitoring of SSS17a/DLT17ck DATE: 17/08/20 13:59:50 GMT FROM: S. J. Smartt at Queens U Belfast K. C. Chambers (IfA), M. E. Huber (IfA),K. W. Smith (QUB), S. J. Smartt, (QUB), D. R. Young, M. Coughlin (Harvard), T.-W. Chen (MPE), J. Bulger, L. Denneau, H. Flewelling, A. Heinze, E. Kankare (QUB), T. Lowe, E. A. Magnier (IfA), A. Rest (STScI), B. Stalder (IfA), A. S. B. Schultz, C. W. Stubbs (Harvard) J. Tonry, C. Waters, R. J. Wainscoat, H. Weiland, M. Willman (IfA), D. E. Wright (QUB) We report continued Pan-STARRS imaging of the transient SSS17a/DLT17ck in NGC4339 in filters i, z and y (see Chambers et al. GCN 21553 for more details of filters, photometry, methods etc). Our reference stack and calibrations provide rapid reliable photometry with the host removed and we will continue to post updates while it is visible from Hawaii. A series of short exposures to avoid sky saturation in twilight in each of i, z, and y provide average nightly magnitudes (AB) of MJD i err 57983.23 17.24 0.06 57984.24 17.91 0.05 57985.24 18.47 0.08 MJD z err 57983.23 17.26 0.06 57984.24 17.80 0.05 57985.24 18.31 0.06 MJD y err 57983.23 17.38 0.10 57984.24 17.59 0.07 57985.24 18.08 0.07 The decline rate 0.6 mag per day is still consistent with some of the kilonova models (Kasen et al. 2015, Barnes & Kasen 2013, Tanaka et al. 2014). The very rapid decline (and weak high energy emission) may explain why transients of these types have not been recovered and recognised independently in ground-based wide-field surveys to date, before the LIGO-Virgo era. For example at d=100Mpc, this transient would fade from around i=19.2 to 21.7 in four days in i-band (and would be fainter and faster in g, r and broad composite filters). Making it difficult to recover and recognise over multiple nights in "~10^3 deg per night" surveys such as PTF, Pan-STARRS, La Silla Quest, Skymapper, CRTS. And well beyond the wider, shallower, ASASSN and ATLAS sensitivities. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21618 SUBJECT: LIGO/Virgo G298048: optical observations of CHILESCOPE observatory DATE: 17/08/20 14:24:47 GMT FROM: Alexei Pozanenko at IKI,Moscow A. Pozanenko (IKI), E. Mazaeva (IKI), A. Volnova (IKI), P. Minaev (IKI), M. Krugov (AFIF) report on behalf of IKI-GW follow-up collaboration: We observed the field of LIGO/Virgo trigger G298048 (LVC GCNs 21509, 21513) and the error circle of GMB/Fermi short burst GRB 170817A (Connaughton et al., GCN 21506) with RC-1000 and ASA-500 telescopes of CHILESCOPE observatory located at W 70d 34m S20d 27m. The observations started on Aug 17 (UT) 23:17:16 in clear filter. The last image was recorded on 2017-08-18T00:59:48. We cover central part of G298048 localization with typical limiting magnitude of 20m at 60 s exposure in each image. The covering map can be found in http://grb.rssi.ru/GRB170817A/bayestar_RC1000%20coverage.png The OT candidate found by Coulter et al. (LVC GCN 21529), the DLT17ck (Sheng Yang et al., GCN 21531) is out of the coverage in the first epoch of the observations. We also cover northern part of GBM/Fermi localization? 1-sigma containment, statistical only (Connaughton et al., GCN 21506). The coverage of the GBM localization is about 20%. Typical limiting magnitude of 17.5m at 60 s exposure in each image. The covering map can be found in http://grb.rssi.ru/GRB170817A/GRB170817A_GBM_coverage_ASA500.png The detailed investigation of the fields is underway. We are grateful to the remote staff of the observatory for timely observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21619 SUBJECT: LIGO/Virgo G298048: TOROS optical counterpart search DATE: 17/08/20 14:48:49 GMT FROM: Martin Bernoiz at TOROS Mario Diaz(UTRGV/CGWA), Diego Garcia Lambas(IATE), Lucas Macri(TAMU), Jose Luis Nilo Castellon To scan the LVC uncertainty region for G298048 we pointed to 14 targets covered in 6 pointings with telescope at La Serena, Chile, filter i, 2 sq deg FoV, 60s integration time. The pointing centers are: 14:00:52.21,-48:23:31.8,2000. 14:12:08.50,-52:43:29.8,2000. 14:06:20.01,-51:04:30.7,2000. 14:05:12.66,-53:17:24.3,2000. 14:19:17.56,-55:22:04.4,2000. 14:18:58.06,-57:59:06.6,2000. Targets covered: PGC141857 : 14:10:33.6,-52:19:02,20" ESO221-030 : 14:10:41.1,-52:11:04,20" PGC448694 : 14:10:37.0,-52:06:06,20" PGC166335 : 14:16:02.0,-53:43:00,20" PGC2800412 : 14:17:10.1,-55:32:39,20" ESO175-002 : 14:08:36.0,-53:21:10,20" ESO221-028 : 14:09:02.2,-51:10:08,20" ESO271-003 : 13:52:27.5,-43:52:53,20" PGC463082 : 14:03:29.3,-50:46:38,20" ESO221-035 : 14:16:04.6,-52:36:31,20" PGC141859 : 14:20:23.5,-55:04:08,20" PGC485499 : 14:03:11.9,-48:37:39,20" ESO271-005 : 13:56:08.4,-45:39:34,20" PGC166323 : 14:04:34.1,-52:41:50,20” The observations started on 2017-08-17T01:37:00 UT and ended on 2017-08-17T04:42:00 UT. Martin Beroiz (UTRGV) on behalf of the TOROS Collaboration. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21620 SUBJECT: LIGO/Virgo G298048: TOROS optical counterpart search (continuation) DATE: 17/08/20 15:03:42 GMT FROM: Martin Bernoiz at TOROS Mario Diaz(UTRGV/CGWA), Diego Garcia Lambas(IATE), Lucas Macri(TAMU), Jose Luis Nilo Castellon. The following tables summarize the observations done to scan the probability region skymap for G298048. The observations we carried over 3 nights, in Tolar Grande, Argentina with a Meade LX 200 GPS 16” telescope. Focal length: 4043mm; FOV : 15,3’x11,5’ and a SBIG STF 8300 camera. 2017-08-16: Exposure time: 30s; Number of images: 123 NGC6397; J2000 : 17h40m41.36s -53d40m25.26s NGC6544; J2000 : 18h07m20.001s -24d59m54.0798s 2017/08/17 Exposure time: 30s NGC6397 : 17h40m41.36s -53d40m25.26s Number of images: 80 NGC6544 : 18h07m20.001s -24d59m54.0798s Number of images: 80 ESO320-007 : 11h35m45.276s -38d21m53.136s Number of images: 15 ESO320-013 ; 11h37m19.884s -38d05m50.748s Number of images: 15 ESO320-019 ; 11h44m45.924s -39d36m55.296s Number of images: 10 ESO320-020 ; 11h46m00.048s -39d20m03.948s Number of images: 10 ESO320-024 ; 11h49m26.004s -38d49m32.988s Number of images: 10 ESO320-027 ; 11h50m24.756s -38d38m56.58s Number of images: 10 ESO320-029 ; 11h52m42.132s -39d27m44.028s Number of images: 12 ESO320-030 ; 11h53m11.76s -39d07m48.648s Number of images: 12 ESO320-031 ; 11h54m06.84s -39d52m03.324s Number of images: 10 ESO320-032 ; 11h54m39.024s -40d55m56.28s Number of images: 10 PGC580951 ; 11h54m59.256s -40d55m26.976s Number of images: 10 ESO320-035 ; 11h56m46.464s -38d11m32.928s Number of images: 12 ESO175-002 :14h08m35.99s -53d21m10.296s Number of images: 20 ESO221-028 :14h09m02.20s -51d10m07.428s Number of images: 22 2017/08/18 Exposure time: 30s NGC6397 : 17h40m41.36s -53d40m25.26s Number of images: 82 NGC6544 : 18h07m20.001s -24d59m54.0798s Number of images: 123 ESO175-002 :14h08m35.99s -53d21m10.296s Number of images: 40 ESO221-028 :14h09m02.20s -51d10m07.428s Number of images: 40 PGC141857 :14h10m33.49s -52d19m01.416s Number of images: 40 PGC448694 :14h10m37.02s -52d06m05.904s Number of images: 40 ESO221-030 :14h10m41.12s -52d11m02.904s Number of images: 33 PGC166335 :14h16m01.99s -53d42m59.4s Number of images: 40 NGC4993 :13h09m48,1s -23d23m53,4s Number of images: 47 Martin Beroiz(UTRGV) on behalf of the TOROS Collaboration. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21621 SUBJECT: LIGO/Virgo G298048: On the kick velocity and age of the binary Neutron Stars Progenitor DATE: 17/08/20 15:40:35 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs V.M.Lipunov, Lomonosov Moscow State University, Sternberg Astronomical Institute There are several very important arguments for reality SSS17a as the kilonova candidate was published in LVC GCN. There are relativictic expansion (see Nichol etal., LVC GCN 21585;) and big distance (delta ~ 3.9Mpc) between host galaxy explositions ( D'Elia et al., LVC GCN 21592). I point out that we can obtain minimal radial space velosity of the progenitor of the G298048: V_min = delta/T_Universe = 3.9 Mpc / 13.7 10^10 yrs ~ 300 km/sec. From other hand, because kick velosity realy is not more than 1000 km/s, we received typical age of the binary NS's as several billion years. This is not contadict to Scenario Machine population synthesis of the NS+NS star merging rates evolution in Universe (Lipunov et al., 1995, Evolution of the Double Neutron Star Merging Rate and the Cosmological Origin of Gamma-Ray Burst Sources,1995, Astrophysical Journal v.454, p.593; Lipunov & Pruzhinskaya; MNRAS, Vol. 440, 1193-1199, 2014. From the other hand diference between NGC 4993 galaxy redshift and Kilonova ( D'Elia et al., LVC GCN 21592) may be explained by fast moving relativistic shell where some absobtion lines can be formed. The NS+NS merging rate evolution from Lipunov et al., 1995 is available at http://master.sai.msu.ru/static/images/green_function.jpg This message can be citted. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21623 SUBJECT: LIGO/Virgo G298048: Kanata/HONIR NIR photometry of the possible counterpart of G298048 DATE: 17/08/20 16:37:38 GMT FROM: Koji S. Kawabata at JGEM T. Nakaoka, K. S. Kawabata, M. Kawabata, H. Nagashima, and Y. Utsumi (Hiroshima University) on behalf of J-GEM collaboration. We performed H-band imaging of the possible counterpart of G298048, SSS17a in NGC 4993 identified by Coulter et al. (LVC GCN 21529), with HONIR on the 1.5-m Kanata telescope at Higashi-Hiroshima Observatory, Japan. Because of low-elevation observation (height~10 deg) during bright twilight, the foreground sky level was still high and SSS17a was considerably faint (~3 sigma) in our stacked image. We performed a forced aperture photometry and estimated a preliminary magnitude in AB system of H = 16.7 (2017 August 20.424-429 UT; MJD 57985.424-429) The magnitude is calibrated against 2MASS field stars. Further analysis is in progress. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21624 SUBJECT: LIGO/Virgo G298048: optical observations with BOOTES-5 at San Pedro Mrtir DATE: 17/08/20 21:59:59 GMT FROM: Alberto J. Castro-Tirado at IAA-CSIC A. J. Castro-Tirado (IAA-CSIC and ISA-UMA), J. C. Tello, Y. Hu, A. Gonzlez-Rodrguez, B.-B. Zhang, R. Cunniffe (IAA-CSIC), W. H. Lee, D. Hiriart (UNAM), S. Jeong and I. H. Park (SKKU), on behalf of a larger collaboration report: In response to the LIGO/Virgo binary neutron star candidate G298048 on Aug 17 (GCNC 21509), we used the JGT 0.6m robotic telescope at the BOOTES-5 station at Observatorio Astronmico Nacional de San Pedro Mrtir (Mxico) to image the 15 galaxies in the GLADE Catalogue (GCN 21516) starting on Aug 18.21 UT. The potential optical candidate (GCN 21529) was only imaged on Aug 19.21 UT, with the images quality being affected by the very high airmass and the twilight sky. The optical candidate (SSS17a) is only barely visible in the outskirts of the NGC 4993 galaxy. A more detailed analysis of the data is in progress. We thank the staff of Observatorio Astronmico Nacional in San Pedro Mrtir. [GCN OPS NOTE(21aug17): Per author's request, (a) the SSS17a name was corrected for a typo, (b) Lee's name was corrected, (c) OAN's name was corrected, and (d) the second paragraph was added.] //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21625 SUBJECT: LIGO/Virgo G298048: ASKAP follow up DATE: 17/08/21 00:58:33 GMT FROM: Tara Murphy at U of Sydney D. Dobie (University of Sydney), A. Hotan (CSIRO), K. Bannister (CSIRO), D. Kaplan (UWM), T. Murphy (University of Sydney), C. Lynch (University of Sydney), on behalf of the ASKAP/VAST collaboration. We are observing the LIGO localisation region (LVC GCN 21513) with the Australian Square Kilometre Array Pathfinder (ASKAP) at a central frequency of 1345 MHz with a bandwidth of 192 MHz. As the array is still undergoing commissioning, we are using a nominal 12 (of 36) antennas, although other site activities may cause that number to vary from one observation to the next. Our observing strategy consists of 3 pointings containing approximately 90% of the LIGO localisation region. Each pointing consists of a 5.5 x 5.5 degree square grid of 36 beams, though the exact number captured may also vary. The first pointing is centered at RA = 13:09:21.60 Dec = -25:00:00.00 and contains ~48% of the localisation region and the positions of 35 target galaxies (Cook et al. LVC GCN 21519) including NGC 4993, the host of the possible optical counterpart SSS17a (Coulter et al. LVC GCN 21529). Observations began at 2017-08-19 05:34:32 (UT) and are ongoing. Processing and analysis of the first pointing is underway. Thank you to CSIRO staff for supporting these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21626 SUBJECT: LIGO/Virgo G298048: NuSTAR limits on X-ray emission DATE: 17/08/21 04:33:27 GMT FROM: Mansi M. Kasliwal at Caltech F. A. Harrison, K. Forster, J. Garcia, B. W. Grefenstette, M. Heida, M. M. Kasliwal, K. K. Madsen, H. Miyasaka, S. Pike, V. Rana, Y. Xu (Caltech) We obtained X-ray imaging of the optical counterpart of SSS17a (Coulter et al.; GCN21529), the candidate optical counterpart of G298048 (LVC; GCN 21509) in the 3 – 79 keV band with NuSTAR. Observations began at 2017-08-18T05:26:09 UT and ended at 2017-08-18T19:46:09, with a total exposure of 24 ksec. We did not detect any X-ray emission in a circular 50’’ extraction region centered on the position of the optical counterpart, with a 3-sigma threshold of 1.4 x 10-14 erg/cm^2/s in the 3-10 keV band, assuming an X-ray spectrum with a photon power law index of -2. No source was detected in the 10-60 keV band, however additional analysis is ongoing to place limits on possible line emission from nuclear decays. We note that the NuSTAR hard X-ray band is not sensitive to X-ray emission from star formation in the host galaxy, and there is no known AGN activity in this source. Further NuSTAR observations are planned. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21627 SUBJECT: LIGO/Virgo G298048: Zadko observations of the OT candidate SSS17a/DLT17ck DATE: 17/08/21 05:57:23 GMT FROM: Eric Howell at U of Western Australia D. Coward (UWA), E. Howell (UWA), R. Laugier (OCA), A. Klotz (UNS-CNRS-OCA), M. Boer (UNS-CNRS-OCA), I. Andreoni (Swinburne), J. Cooke (Swinburne), D. Macpherson (UWA), J. Moore (UWA) and A. Burrell (UWA) report on behalf of OzGrav and TZAC (see acknowledgements below): We report Zadko Telescope imaging of the transient SSS17a/DLT17ck in NGC4339 started at 2017-08-20 10:59 UT. In a preliminary analysis using background subtraction of the host galaxy NGC4339 through rotational masking, a photometric calibration using the star NOMAD-10666-0296310 (R=17.35) yields a magnitude of the optical transient R=20.05 +/- 0.15. Acknowledgments: The Zadko Telescope is operated by the University of Western Australia (UWA), and was made possible by a philanthropic donation by James Zadko to UWA. The facility receives support from the ARC Centre of Excellence "OzGrav" for gravitational wave follow-up and discovery. Key personnel include D.Coward (Director-UWA), E. Howell (UWA), J. Moore (UWA), A. Burrel (UWA), A. Greensky, J. Kennewell with collaborators I. Andreoni and J. Cooke (Swinburne). This observation report was done in partnership with the LIGO follow-up collaboration TZAC, which is supported by M. Boer, A. Klotz, R. Laugier, K. Noysena //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21628 SUBJECT: LIGO/Virgo G298048: ATCA 8.5 GHz observations of galaxies in the localisation volume DATE: 17/08/21 07:45:30 GMT FROM: Tara Murphy at U of Sydney C. Lynch (University of Sydney), T. Murphy (University of Sydney), D. Kaplan (UWM), K. Bannister (CSIRO), D. Dobie (University of Sydney) on behalf of the VAST collaboration. We have observed 54 galaxies in the localisation volume of G298048 as listed by Cook et al. (LVC GCN 21519) with the Australia Telescope Compact Array at 8.5 GHz (Bannister et al. LVC GCN 21537). The observations were taken in the EW352 configuration, with approximately 1-2 minutes on each source between 2017-08-18 01:00 UT and 2017-08-18 09:14:15 UT. We detected 8.5 GHz radio emission from 5 galaxies, as listed below: Galaxy 3-sigma flux density UGCA 331 0.33 mJy NGC 4993 0.66 mJy NGC 4968 16.1 mJy IC 4197 2.7 mJy ESO 508- G 033 3.7 mJy The rest of the sources in the list were non-detections. We list 3-sigma upper limits on the 8.5 GHz radio emission below: Galaxy 3-sigma flux density limit IC 3825 102.8 uJy ABELL 1631:[CZ2003]B0295[024] 47.1 uJy GALEXASC J125157.02-160617.8 43.7 uJy MCG -02-33-036 24.9 uJy 2MASX J12525109-1529300 33.2 uJy GALEXASC J125301.39-151007.7 36.9 uJy WINGS J125412.84-153523.6 25.9 uJy 6dF J1254495-160308 36.2 uJy GALEXASC J125520.46-170546.9 33.6 uJy HIPASS J1255-15 36.5 uJy ESO 575- G 029 46.8 uJy MCG -03-33-023 198.8 uJy WINGS J125701.38-172325.2 213.4 uJy NGC 4830 60.0 uJy GALEXASC J125811.97-210246.3 22.6 uJy GALEXASC J130415.26-225251.3 21.2 uJy ESO 575- G 053 50.4 uJy 6dF J1305235-233121 18.2 uJy GALEXASC J130525.30-233008.8 12.8 uJy 2MASX J13061939-2258491 77.5 uJy ESO 508- G 003 60.3 uJy ESO 575- G 055 85.7 uJy ESO 508- G 004 66.2 uJy UGCA 325 35.0 uJy GALEXASC J130707.37-240634.4 35.0 uJy NGC 4970 48.5 uJy ABELL 1664_11:[PSE2006] 2506 54.7 uJy ESO 508- G 010 39.2 uJy UGCA 327 39.8 uJy USGC S204 44.5 uJy HDCE 0763 39.2 uJy ESO 508 62.8 uJy ESO 508- G 014 56.0 uJy 2MFGC 10461 44.3 uJy 6dF J1309177-242256 24.6 uJy GALEXASC J130918.58-242304.8 25.6 uJy UGCA 328 23.1 uJy ESO 576- G 003 49.4 uJy [TSK2008] 0073 32.2 uJy GALEXASC J131426.62-271242.6 53.4 uJy [TSK2008] 0052 56.6 uJy ESO 508- G 035 70.5 uJy We have not yet been able to make reliable measurements for the following 7 sources, so they are excluded from the above lists: 2MASX J12505229-1454238 2MASX J12573271-1942006 2MASX J13073768-2356181 GALEXASC J125259.36-152150.9 IC 4180 2MFGC 10484 ESO 508- G 019 We did not observe GALEXASC J120652.88-040236.6. Further observations are underway. Thank you to CSIRO staff for supporting these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21629 SUBJECT: LIGO/Virgo G298048: Correction to ATCA 8.5 GHz observations DATE: 17/08/21 09:02:12 GMT FROM: Tara Murphy at U of Sydney C. Lynch (University of Sydney), T. Murphy (University of Sydney), D. Kaplan (UWM), K. Bannister (CSIRO), D. Dobie (University of Sydney) on behalf of the VAST collaboration. We report a correction to the radio upper limits announced in GCN 21628. All values are the 1-sigma limits at the location of each source, not the 3-sigma limits as stated. We apologise for the error. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21631 SUBJECT: LIGO/Virgo G298048 ANTARES search (2) DATE: 17/08/21 15:08:00 GMT FROM: Damien Dornic at CPPM/CNRS M. Ageron (CPPM/CNRS), B. Baret (APC/CNRS), A. Coleiro (IFIC & APC), D. Dornic (CPPM/CNRS), A. Kouchner (APC/Universite Paris Diderot), T. Pradier (IPHC/Universite de Strasbourg) report on behalf of the ANTARES Collaboration: The refined location of the LIGO/Virgo G298048 event (90% confidence level contour Bayestar-HLV) falls outside the optimum field of view of ANTARES (as defined with upward going events). GCN #21522 reported the results of the upward going neutrino search. As a consequence, we have performed a dedicated analysis looking for down-going neutrino candidates in the on-line ANTARES data stream. Cuts on the quality of the track reconstruction and an energy proxy have been used to reduce the false alarm rate in such a way that one event matching in time (+/- 500 s) and direction (90% C.L contour) with G298048 would result in a 3-sigma excess. The ANTARES visibility, for down-going events, at the time of the alert together with the 90% contour of the probability map are shown in: https://www.cppm.in2p3.fr/~dornic/events/G298048/gw190817_visi_down.png (gwantares/GW@ANT31). No down-going muon neutrino candidate events were recorded by ANTARES within the 90% C.L. contour and during a +/- 500 s time-window centered on the G298048 event time. An extended search during +/- 1 hour yields no coincidence. An estimate of the upper limit on the associated neutrino fluence will be sent in a subsequent circular. ANTARES, being installed in the Mediterranean Deep Sea, is the largest neutrino detector in the Northern Hemisphere. It is primarily sensitive to astrophysical neutrinos in the TeV-PeV energy range. At 10 TeV, the median angular resolution for muon neutrinos is below 0.5 degrees. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21632 SUBJECT: LIGO/Virgo G298048: Continued monitoring of the optical counterpart candidate DATE: 17/08/21 15:49:41 GMT FROM: Myungshin Im at Seoul National U M. Im, C. Choi, J. Kim, Lim, G. H. M. Lee (SNU), S.-L. Kim, C.-U. Lee (KASI) on behalf of the KU collaboration We continued to monitor the strong optical counterpart candidate of LIGO/Virgo G298048 (GCNs 210505, 21509, 21513), SSS17a/DLT17ck(Coutler et al. GCN 21529; Allam et al. GCN 21530; Yang et al. GCN 21531; Arcavi et al. GCN 21538; also see notes below for a list of optical/NIR observation reports). The observation was carried out using three KMTNet 1.6m telescopes and other small telescopes (Im et al. GCNs 21563, 21566, 21597) at three sites , the Siding Spring Observatory (SSO), the South African Astronomical Observatory (SAAO), and the Cerro-Tololo Inter-American Observatory (CTIO). We imaged the object with B,V,R,I,i,z, filters and medium-band images at 825, 875, 925, 975 nm. We confirm that the object is fading in optical and its continuum shape has been becoming redder as time goes on (e.g., Cenko et al. GCN 21572; Lyman et al. GCN 21582; Wiseman et al. GCN 21584; Chambers et al. GCN 21590; Malesani et al. GCN 21590; Chen et al. GCN 21608). A part of the data from several sites are presented below. UT V R I Site 08-18.72 17.8(0.1) 17.4(0.1) 17.3(0.1) SAAO 08-18.99 18.3(0.1) 17.6(0.1) 17.4(0.1) CTIO 08-19.72 19.4(0.1) 18.3(0.1) 17.9(0.1) SAAO 08-19.98 19.8(0.1) 18.4(0.1) 18.2(0.1) CTIO The observations and further analysis of the data are ongoing. Notes: It is remarkable that more than 40 optical/NIR follow-up imaging/spectroscopic observations of the optical counterpart candidates have been reported in three days since the first discovery report of the optical counterpart. For reference, we list them here (let me know if I am missing any). They are, Coutler et al. (GCN 21529, 21567), Allam et al. (GCN 21530), Yang et al. (GCNs 21531, 21579), Melandri et al. (GCN 21532, 21596), Arcavi et al. (GCNs 21538, 21565, 21581), Nicholl et al. (GCN 21541, 21580, 21585), Tanvir et al. (GCN 21544), Lipunov et al. (GCNs 21546, 21570, 21587), Drout et al. (GCN 21547), Evans et al. (GCN 21550), Simon et al. (GCN 21551), Singer et al. (GCN 21552), Chambers et al. (GCN 21553, 21590, 21617), Wolf et al. (GCN 21560), Yoshida et al. (GCN 21561, 21586), Im et al. (GCNs 21563, 21566, 21597), Cenko et al. (GCN 21572), Lyman et al. (GCN 21582), Kilpatrick et al. (GCN 21583), Wiseman et al. (GCN 21584), Malesani et al. (GCN 21591), D’Elia et al. (GCN 21592), Wiersema et al. (GCN 21594), Tominaga et al. (GCN 21595), Valenti et al. (GCN 21606), Chen et al. (GCN 21608), Pozanenko et al. (GCN 21618), Nakaoka et al. (GCN 21623), Castro-Tirado et al. (GCN 21624), Coward et al. (GCN 21627). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21633 SUBJECT: LIGO/Virgo G298048: Pan-STARRS izy photometry of SSS17a/DLT17ck DATE: 17/08/21 16:03:52 GMT FROM: S. J. Smartt at Queens U Belfast K. C. Chambers (IfA), M. E. Huber (IfA),K. W. Smith (QUB), S. J. Smartt, (QUB), D. R. Young, M. Coughlin (Harvard), T.-W. Chen (MPE), J. Bulger, L. Denneau, H. Flewelling, A. Heinze, E. Kankare (QUB), T. Lowe, E. A. Magnier (IfA), A. Rest (STScI), B. Stalder (IfA), A. S. B. Schultz, C. W. Stubbs (Harvard) J. Tonry, C. Waters, R. J. Wainscoat, H. Weiland, M. Willman (IfA), D. E. Wright (QUB) We report continued Pan-STARRS imaging of the transient SSS17a/DLT17ck in NGC4339 in filters i, z and y (see Chambers et al. GCN 21553 for more details of filters, photometry, methods etc). Our reference stack and calibrations provide rapid reliable photometry with the host removed and we will continue to post updates while it is visible from Hawaii. A series of short exposures to avoid sky saturation in twilight in each of i, z, and y provide average nightly magnitudes (AB) as follows. Pan-STARRS is observing at lower altitude than it has ever done, Poor conditions and airmass>3 hampered the fourth night of observing (57986 = 2017-08-21 UT). The difference images showed faint flux in z band, but no detection in i and y. The forced photometry in the z-band at the position of the transient is reported. The quick estimates for i and y need to be verified. MJD i err 57983.23 17.24 0.06 57984.24 17.91 0.05 57985.24 18.47 0.08 57986.24 <18.5 limit only MJD z err 57983.23 17.26 0.06 57984.24 17.80 0.05 57985.24 18.31 0.06 57986.24 18.27 0.33 MJD y err 57983.23 17.38 0.10 57984.24 17.59 0.07 57985.24 18.08 0.07 57986.23 <18.0 limit only //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21634 SUBJECT: LIGO/Virgo G298048: TOROS Spectra observation with CASLEO DATE: 17/08/21 16:05:22 GMT FROM: Martin Bernoiz at TOROS Mario Diaz(UTRGV/CGWA), Diego Garcia Lambas(IATE), Lucas Macri(TAMU), Jose Luis Nilo Castellon(Univ La Serena) We report a spectrum observation of SSS17a in CASLEO Observatory, Argentina. Telescope: Jorge Sahade Reflector Ritchey Chretien Primary mirror diameter: 2153 m Geographic coordinates: Lon = W 69 18 23.16 Lat = -31 47 14.46 Reosc Spectrograph Diffraction grating of 300 lin/mm (blaze at 500 nm) Simple dispersion configuration Slit width of 350 microns = 1 arcsec Spectral Resolution: 13.5 Angstrom Slit Orientation: E-W Observations performed on 08/19/2017 (the night of 18) starting at approximately 00:15 UTC finishing at approximately 01:30 UTC Performed 3 integrations of 1200 seconds Atmospheric conditions: clear sky; seeing approx. >2 arcsec Martin Beroiz on behalf of TOROS Collaboration. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21635 SUBJECT: LIGO/Virgo G298048: observations of optical counterpart candidate with CHILESCOPE observatory DATE: 17/08/21 16:11:53 GMT FROM: Alexei Pozanenko at IKI,Moscow A. Pozanenko (IKI), A. Volnova (IKI), E. Mazaeva (IKI), P. Minaev (IKI), M. Krugov (AFIF) report on behalf of IKI-GW follow-up collaboration: We observed the possible counterpart SSS17a/DLT17ck (Coulter et al. GCN 21529; Yang et al., GCN 21531) of LIGO/Virgo trigger G298048 (LVC GCNs 21509, 21513) with RC-1000 telescope of CHILESCOPE observatory. The observations carried out in clear filter in two epochs, on Aug. 19 and Aug.20. Photometry of the transient SSS17a/DLT17ck is following Date UT start Filter OT Err UpLim (3 sigma) 2017-08-19 23:30:33 CR 16.7 0.2 21.9 2017-08-20 23:21:09 CR 18.5 0.2 22.0 The photometry is based on several nearby USNO-B1.0 stars (R2). The photometry is still preliminary and required careful estimation of NGC4339 influence. Nevertheless it is evident the source is fading significantly which is confirmed by many observations (e.g. Im et al., GCN 21632 and references in the GCN 21632). We are grateful for the team of remote controlled CHILESCOPE observatory (www.chilescope.com) for observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21636 SUBJECT: LIGO/Virgo G298048: VLA observation at 15 GHz DATE: 17/08/21 18:40:08 GMT FROM: Alessandra Corsi at Texas Tech U. A. Corsi (TTU) and M.M. Kasliwal (Caltech) report on behalf of a larger collaboration: We analyzed the Karl G. Jansky VLA observation of the field of the possible optical counterpart SSS17a (Coulter et al. LVC GCN 21529) that started on 2017-Aug-19 22:01:48 UT (Corsi et al. LVC GCN 21613). At a central frequency of ~15 GHz, our preliminary analysis does not show evidence for significant emission at the location of the optical candidate (RA= 13:09:48.089, Dec= -23:22:53.35, Coulter et al. LVC GCN 21529) down to a 3-sigma limit of ~16 uJy. The host galaxy (RA = 13:09:47.704, Dec =-23:23:02.45; Alexander et al. LVC GCN 21589) is clearly detected (flux level of ~0.25 mJy at 15 GHz). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21637 SUBJECT: LIGO/Virgo G298048: MWA Observations of Error Region DATE: 17/08/22 00:59:36 GMT FROM: David Kaplan at UW-Milwaukee D. Kaplan (UWM), M. Sokolowski (Curtin University), R. Wayth (Curtin University), T. Murphy (University of Sydney), D. Dobie (University of Sydney), C. Lynch (University of Sydney), and K. Bannister (CSIRO) on behalf of the MWA collaboration. We have observed a 20 x 20 deg field-of-view centered on the LIGO/Virgo G298048 localization region (LVC GCN #21513) with the Murchison Widefield Array. Observations occurred on 2017-08-18, 2017-08-19, 2017-08-20, 2017-08-21, and 2017-08-22, all from roughly 07:00 UT to 09:30 UT, at a central frequency of 185 MHz. Note that the array is in the process of being reconfigured, so only 5/16 of the tiles are operational. Analysis of this data is underway, and subsequent epochs are planned. We thank the MWA Operations team for supporting these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21638 SUBJECT: LIGO/Virgo G298048: Gemini-South Near-Infrared Spectroscopy DATE: 17/08/22 05:20:11 GMT FROM: Ryan Chornock at Ohio U R. Chornock (Ohio University) and E. Berger (Harvard) report on behalf of a larger collaboration: We have been obtaining a sequence of near-infrared spectroscopy (range 1-1.8 microns) of the optical counterpart (SSS17a: Coulter et al., GCN 21529; Allam et al., GCN 21530) of LIGO/Virgo G298048 (GCNs 21509, 21513) using FLAMINGOS2 on Gemini-South (PI: Chornock). Our initial spectra, taken on 20170819 at 00:45 UT (~1.5 days after the LIGO/Virgo event) have a smooth blue continuum. Data taken the following night show a few broad, low-amplitude features starting to develop. An initial reduction of data taken on 20170821 at 23:40 UT (~4.5 days after the LIGO/Virgo event) shows that these features (including a possible spectral peak near 1.05 microns) have strengthened. Analysis is ongoing and further observations are planned to constrain the potential presence of lanthanide opacities in the near-infrared. We thank the Gemini staff, particularly Hwihyun Kim, Gonzalo Diaz, Pablo Candia, and Laura Ferrarese for their support of these operations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21639 SUBJECT: LIGO/Virgo G298048: ASKAP observations of SSS17a and NGC 4993 at 1.345 GHz DATE: 17/08/22 07:23:04 GMT FROM: Tara Murphy at U of Sydney D. Dobie (University of Sydney), A. Hotan (CSIRO), K. Bannister (CSIRO), T. Murphy (University of Sydney), D. Kaplan (UWM), C. Lynch (University of Sydney), on behalf of the ASKAP/VAST collaboration. We have observed the LIGO/Virgo localisation region (LVC GCN 21527) with the Australian Square Kilometre Array Pathfinder (ASKAP) at a central frequency of 1.345 GHz with a bandwidth of 192 MHz. Observations started at 2017-08-19 05:34 UT and ended at 2017-08-19 07:58 UT. We do not detect any emission at the position of the possible optical counterpart SSS17a (Coulter et al. LVC GCN 21529), or its candidate host galaxy NGC 4993. The upper limit for NGC 4993 is consistent with a spectral index of -0.7 found by fitting the measured results from the ATCA (Bannister et al. LVC GCN 21559) between 8.5 and 21.2 GHz. Further analysis of our observations is ongoing. Thank you to CSIRO staff for supporting these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21641 SUBJECT: LIGO/Virgo G298048: CALET Observations DATE: 17/08/22 09:36:51 GMT FROM: Takanori Sakamoto at Aoyama Gakuin U S. Nakahira (RIKEN), A. Yoshida, T. Sakamoto, Y. Kawakubo, M. Moriyama, Y. Yamada, A. Tezuka, S. Matsukawa (AGU), K. Yamaoka (Nagoya U), I. Takahashi (IPMU), Y. Asaoka, S. Ozawa, S. Torii (Waseda U), Y. Shimizu, T. Tamura (Kanagawa U), W. Ishizaki (ICRR), M. L. Cherry (LSU), S. Ricciarini (U of Florence), A. V. Penacchioni, P. S. Marrocchesi (U of Siena) and the CALET collaboration: The CALET Gamma-ray Burst Monitor (CGBM) was operating at the trigger time of G298048 (The LIGO Scientific Collaboration and the Virgo Collaboration, GCN Circ. 21509). No CGBM on-board trigger occurred at the time of the event. Based on the updated LVC localization sky map (preliminary-LALInference.fits.gz), none of the probability area was in the field-of-view of the CGBM/HXM. However, 99% of the summed probability was inside the field-of-view of the CGBM/SGM. The CGBM/SGM boresight position (R.A., Dec. = 223.8 deg, 43.4 deg) was 73 deg off-axis from the maximum LVC probability location (The LIGO Scientific Collaboration and the Virgo Collaboration, GCN Circ. 21527). Based on the analysis of the light curve data with 0.125 sec time resolution from -60 sec to 60 sec from the trigger time, we found no significant excess around the trigger time in either the HXM (7-3000 keV) or the SGM (40 keV -28 MeV) data. The incident angle of SGM to the position of SSS17a (Coulter et al., GCN Circ. 21529) was 71 deg. Assuming the association of GRB 170817A (Connaughton et al., GCN Circ. 21506) and SSS17a, we estimated the upper limit of the SGM. The 7-sigma upper limit of SGM using alpha=-0.9 and Epeak=130 keV (Goldstein et al., GCN Circ. 21528) is 5.5e-7 erg/cm2/s in the 10-1000 keV band at 1 s exposure assuming no shielding by ISS structures. This estimated upper limit is at the similar level to the reported peak flux, 7.3e-7 erg/cm2/s, of GRB 170817A by Fermi-GBM. We further noticed that the position of SSS17a was covered by the large structure of ISS at the time of the trigger. Because of this, the SGM sensitivity should be worse than what we reported above. Therefore, it is consistent that no signal of GRB 170817A is seen by the SGM data. The CALET Calorimeter (CAL) was operating in the high energy trigger mode at the trigger time of G298048. However, no LVC high probability region was included in the CAL's field of view at the time of the trigger. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21644 SUBJECT: LIGO/Virgo G298048: observations of optical counterpart candidate with CHILESCOPE observatory DATE: 17/08/22 15:23:04 GMT FROM: Alexei Pozanenko at IKI,Moscow A. Pozanenko (IKI), A. Volnova (IKI), E. Mazaeva (IKI), P. Minaev (IKI), M. Krugov (AFIF) report on behalf of IKI-GW follow-up collaboration: We continue observation of the possible counterpart SSS17a/DLT17ck (Coulter et al. GCN 21529; Yang et al., GCN 21531) of LIGO/Virgo trigger G298048 (GCNs 21509, 21513) with RC-1000 telescope of CHILESCOPE observatory. The observations carried out in clear filter starting on Aug. 21 (UT) 23:32:09. Preliminary Photometry of the transient SSS17a/DLT17ck is following Date UT start MJD Filter OT Err UpLim (3 sigma) 2017-08-21 23:32:09 57987.00386 CR 18.8 0.2 22.2 The photometry is based on several nearby USNO-B1.0 stars (R2). The photometry is still preliminary and required careful estimation of NGC4339 influence. We are grateful for the team of remote controlled CHILESCOPE observatory (www.chilescope.com) for observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21645 SUBJECT: LIGO/Virgo G298048: Global properties and star-formation rate of NGC 4993 DATE: 17/08/22 16:55:17 GMT FROM: David Kaplan at UW-Milwaukee E. M. Sadler (University of Sydney), J. R. Allison (University of Sydney), D. L. Kaplan (UWM), T. Murphy (University of Sydney) on behalf of the VAST collaboration. The global properties of the candidate host galaxy NGC 4993 appear entirely consistent with those of a normal early-type galaxy, with a negligible level of ongoing star formation. An archival optical spectrum from the 6dF Galaxy Survey (6dFGS; Jones et al. 2009) is dominated by the light of an old stellar population along with weak H-alpha and [NII] emission lines. The relatively high [NII]/H-alpha emission-line ratio is suggestive of a low-ionisation AGN rather than star formation. The galaxy is devoid of any large neutral gas reservoir, with an upper limit to the neutral hydrogen mass of M_HI < 2e9 Msun (HIPASS; Meyer et al. 2004). The 6dFGS fibre (6 arcsecond diameter) only covers the central region of the galaxy, and excludes the location of the putative optical counterpart, so it is still possible that star formation could be occurring outside the region covered by the 6dFGS spectrum. To check this, we looked at several photometric indicators of the current rate of massive star formation across the galaxy as a whole. We caution that all the values derived here should be considered as upper limits because of the possibility of contamination from a central AGN. From GALEX photometry (S_NUV ~ 1.08e-4 Jy) we obtain a near UV luminosity of L_NUV ~ 1.9e19 W/Hz. Using the relations from A. Hopkins (PhD thesis) and Cowie et al. (1997) gives an estimated NUV-derived star formation rate of SFR(NUV) ~ 0.003 Msun/yr for massive stars with M > 5 Msun. This low star formation rate is consistent with the global upper limit from far infrared photometry. NGC 4993 is undetected by IRAS, so we adopt a conservative upper limit of 0.25 Jy for the FIR flux density at 60 microns. This gives a 60 micron luminosity L_FIR < 4.3e22 W/Hz. From Condon et al. (1992), this translates to a star formation rate (for stars more massive than 5 Msun) of SFR(FIR) < 0.08 Msun/yr. The existence of a low-luminosity radio-emitting active galactic nucleus in this galaxy is not surprising. The bivariate radio luminosity function of Mauch & Sadler (2007) implies that approximately 10% of galaxies of similar stellar mass to NGC 4993 host a radio AGN at least as strong as the central radio source reported for NGC 4993 (LVC GCNs 21537, 21548, and others), so the presence of this source is not unusual. The nuclear dust lanes evident in the HST ACS images (Foley et al. LVC GCN 21536) are similar to those seen in many other early-type galaxies, and may be the product of a minor merger than occurred as long as several Gyr ago. In summary, there is persuasive evidence that the current rate of massive-star formation in NGC 4993 is very low. We therefore speculate that the massive-star progenitors of the binary neutron-star system are likely to have formed and exploded several Gyr ago, implying a long in-spiral time for the neutron-star pair that produced the GW event. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21648 SUBJECT: LIGO/Virgo G298048: Chandra X-ray observations DATE: 17/08/22 18:06:23 GMT FROM: Raffaella Margutti at Northwestern U R. Margutti, W. Fong (Northwestern), E. Berger (Harvard), R. Chornock (Ohio University), P. Cowperthwaite, K. D. Alexander (Harvard) We observed the field of the EM counterpart to the LVC trigger G298048 with the Chandra X-ray Observatory (CXO) starting on 2017-08-19T17:10:09UT (PI Fong). We do not find evidence for significant X-ray emission at the location of the optical transient (RA= 13:09:48.08, Dec= -23:22:53.2, Coulter et al. LVC GCN 21529; Allam et al., LVC GCN 21530; Sheng Yang et al., LVC GCN 21531; Chambers et al. LVC GCN 21553). An extended X-ray source is clearly detected at: RA= 13:09:47.7 dec= -23:23:02.0 This position is consistent with the radio source that we identified in Alexander et al. (LVC GCN 21589) and it is centered on the host-galaxy optical position. Based on preliminary analysis, we estimate a flux ~1e-14 erg/s/cm2 in the 0.3-10 keV band. The CXO X-ray source lies outside the 90% containment, but within the 3-sigma containment, of the localization region of the Swift-XRT source (Evans et al., LVC GCN 21612). The flux inferred by Evans et al., Fx=2.6 (+1.1, -0.9) e-14 erg/cm^2/s is also consistent with our results. We thus suggest that the X-ray source identified by Swift-XRT is most likely emission from the host galaxy. We thank Belinda Wilkes and the entire Chandra team for their great support with these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21650 SUBJECT: LIGO/VIRGO G298048: VLA/JAGWAR observations of the CLU galaxies DATE: 17/08/22 19:13:38 GMT FROM: Kunal Mooley at U of Oxford K. P. Mooley (Hintze Fellow, Oxford) and G. Hallinan (Caltech) report on behalf of the JAGWAR team We have initiated deep S band (2-4 GHz) observations of the potential host galaxies of the GW event G29048 from the CLU list (Cook et al. 2017, LVC GCN 21535). The pointings, observed as part of the Jansky Array mapping of GW bursts as Afterglows in Radio (JAGWAR) program, have RMS noise between 10-20 uJy. The first observing epoch of NGC 4993 on 2017 Aug 20.93 shows no radio source at the location of SSS17a (Coulter et al. 2017, LVC GCN 21529), with a 3sigma upper limit of ~40 uJy. We will report any radio transients found through the LVC GCN system. We thank the VLA staff for scheduling these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21653 SUBJECT: LIGO/Virgo G298048: ESO/VLT optical observations DATE: 17/08/23 07:52:38 GMT FROM: Paolo D'Avanzo at INAF-OAB P. D'Avanzo, A. Melandri, S. Covino (INAF-OAB), M. G. Bernardini (LUPM/INAF-OAB), M. Branchesi (GSSI), S. Campana (INAF-OAB), V. D'Elia (INAF-ASDC), M. Della Valle (INAF-OAC), Y. Z. Fan (PMO, Nanjing), G. Ghirlanda, G. Ghisellini (INAF-OAB), L. Nava (INAF-OATs/INAF-OAB), E. Palazzi (INAF-IAFS Bo), A. Pescalli (Univ. Insubria/INAF-OAB), T. Piran (HUJI), S. Piranomonte (INAF-OAR), O. S. Salafia (Univ. Bicocca/INAF-OAB), R. Salvaterra (INAF-IASF Mi), G. Stratta (Urbino University/INFN Firenze), G. Tagliaferri (INAF-OAB), E. Troja (NASA-GSFC), S. D. Vergani (Obs. Paris/CNRS/INAF-OAB), Z. P. Zhin (PMO, Nanjing), and G. Greco (Urbino University/INFN Firenze), D. Fugazza (INAF-OAB), L. Amati (INAF-IASF Bo), L. A. Antonelli, (INAF-OAR), S. Ascenzi (INAF-OAR), S. Benetti (INAF-OAPD), M.T. Botticella (INAF-OAC), E. Cappellaro (INAF-OAPD), F. Getman (INAF-OAC), A. Grado (INAF-OAC), L. Limatola (INAF-OAC), M. Lisi (INAF-OAR), L. Nicastro (INAF-IASF Bo), E. Pian (SNS-Pisa), L. Pulone (INAF-OAR), A. Rossi (INAF-IASF Bo), V. Testa (INAF-OAR), L . Tomasella (INAF-OAPD), S. Yang (INAF-OAPD), E. Brocato (INAF-OAR) on behalf of GRavitational Wave Inaf TeAm report: We observed the transient SSS17a in NGC 4993 reported by Coulter et al. (LVC GCN 21529) with the ESO/VLT UT1 equipped with the FORS2 camera. Imaging observations were carried out on 2017 Aug 21 starting at 23:23:10 UT during twilight (about 4.5 days after the LIGO/Virgo event; LVC GCNs 21509) with the B, V, R, I and z filters. The source is detected in all bands, showing a red color. From preliminary photometry (likely contaminated by the host galaxy light) we measure the following AB magnitudes: R = 19.4 +/- 0.2 z = 18.5 +/- 0.2 calibrated against the USNOB1 and PAN-STARRS catalogues. We acknowledge excellent support from the from the ESO observing staff in Paranal, in particular Jesus M. Corral-Santana and Stephane Brillant. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21664 SUBJECT: LIGO/Virgo G298048: Continued VLA monitoring at 6 GHz DATE: 17/08/23 18:25:07 GMT FROM: Alessandra Corsi at Texas Tech U. A. Corsi (TTU), M.M. Kasliwal (Caltech), D. Frail (NRAO), and N.T. Palliyaguru (TTU) report on behalf of a larger collaboration: We observed the field of SSS17a/DLT17ck (e.g., Coulter et al. LVC GCN 21529; Allam et al. LVC GCN 21530; Yang et al. LVC GCN 21531), the possible counterpart of G298048 (LVC, LVC GCN 21505) in NGC 4993, with the Karl G. Jansky VLA. The observation lasted 1 hr, centered on 2017-Aug-22.88 UT, and was conducted in C-band (approximate central frequency of 6 GHz). Our preliminary analysis does not show evidence for significant emission at the location of the optical candidate SSS17a/DLT17ck, down to a 3-sigma limit of about 20 uJy. Further observations are planned. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21669 SUBJECT: LIGO/Virgo G298048: Properties of NGC 4993 DATE: 17/08/24 01:39:20 GMT FROM: Mansi M. Kasliwal at Caltech Po-Chieh Yu (NCU), C.-C. Ngeow (NCU), W.-H. Ip (NCU) on behalf of the GROWTH (Global Relay of Observatories Watching Transients Happen collaboration) Ogando et al. (2008) measured velocity dispersion and Lick indices for the candidate host galaxy NGC 4993 using long-slit spectra obtained with the 1.52m ESO telescope. From their measurements of the central velocity dispersion (163 km/s), we obtained the central black holes mass of log(Mbh/Msun) ~ 7.7 using the relation given by Ferrarese & Merritt (2000). We decomposed Pan-STARRS stacked r-band image of the galaxy using Galfit (Peng et al. 2010). Our initial analysis obtained that the Sersic index n =1.27. Using the Mbh-n relation (Savorgnan et al. 2013) gives a similar estimation of the black hole mass log(Mbh/Msun) = 7.25. We also obtained the effective radius Re = 2.8 kpc; the OT is located at ~2.2 kpc (0.78 Re) from the nucleus. We estimated the bolometric luminosity L_bol = 8.96e40 erg/s by adopting Lx=5.6e39 erg/s (Evans et al. LVC GCN 21612) and using bolometric correction Lbol/Lx = 16 for low-luminosity AGNs (LLAGNs; Ho 2008). We obtained the Eddington luminosity L_Edd = 1.26e45.7 erg/s by using the Mbh = 10e7.7 Msun given in this circular. This gives the Eddington ratio L_bol/L_Edd = 7e(-5.7), which is similar to ratios of other LLAGNs (Ho 2008). The galaxy has 18 companions, and it is considered to be located in medium density regions (4 < N < 22) (Ogando et al. 2008). The galaxy mass estimated by the effective radius and the central velocity dispersion (Burstein et al.1997) is log(M*/Msun)=10.64, which is similar to the mean value of the S0 sample of Ogando et al. (2008). Our residual image of subtracting an IRAF elliptical model from the HST archival ACS image (F606W) shows clearly complicated dust lanes that are extended from the nucleus to outer kpc regions, as mentioned in Foley et al. (LVC GCN 21536). NGC 4993 could be a radio AGN (LVC GCN 21537, 21548, 21645). HST images show that some radio galaxies have optical jets (M87, 3C15, 3C78, 3C264). But no optical jets can be seen in our residual map of NGC 4993. In summary, the properties of the candidate host galaxy NGC 4993 seem to be similar to normal early type galaxies, as indicated by Sadler et al. (LVC GCN 21645). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21670 SUBJECT: LIGO/Virgo G298048: ATCA follow-up of SSS17a in NGC 4993 DATE: 17/08/24 04:30:05 GMT FROM: Tara Murphy at U of Sydney C. Lynch (University of Sydney), T. Murphy (University of Sydney), D. Kaplan (UWM), K. Bannister (CSIRO), D. Dobie (University of Sydney) on behalf of the VAST collaboration. Following Bannister et. al. (LVC GCN 21559) and Kaplan et al. (LVC GCN 21574), we observed a second epoch of NGC 4993 with the Australia Telescope Compact Array at 8.5 and 10.5 GHz. Observations started at 2017-08-20 23:31:02.9 UT and ended at 2017-08-21 11:20:00 UT with approximately 13 minutes of on-source time. We fit and subtracted a point-source at the optical position of NGC 4993 (13:09:47.71, -23:23:01.79; Skrutskie et al. 2003, 2MASS Extended Source Catalog). From this we set a 3-sigma upper limit of 135 uJy and 99 uJy on radio emission from SSS17a at 8.5 and 10.5 GHz respectively. Subsequent epochs are planned. Thank you to CSIRO staff for supporting these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21671 SUBJECT: LIGO/Virgo G298048: Results of the ASKAP search for fast radio bursts DATE: 17/08/24 06:10:24 GMT FROM: Keith Bannister at ATNF K. Bannister (ATNF), R. Shannon (ATNF/ICRAR/Curtin University), A. Hotan (ATNF), C. James (ICRAR/Curtin University/CAASTRO), S. Oslowski (Swinburne University), W. Farah (Swinburne University). We observed the 90% containment region of the Bayestar map (Singer et al. LVC GCN 21513) with 7 antennas of the The Australian Square Kilometer Array Pathfinder (ASKAP). We recorded fast autocorrelation data with 336 x 1 MHz channels and a time sampling of 1.26 ms centered at 1320 MHz (see [1] for observing details). We used flys-eye observing mode, with some parts of the field covered by 2 antennas and some by 1 antenna. We had 3 observing runs with start times (UTC) and durations as shown below: 2017-08-18 04:05 3.6 hrs 2017-08-18 08:57 4.1 hrs 2017-08-19 02:08 11.0 hrs We searched out to a dispersion measure of 2000 pc/cm3 and width boxcar widths from 1 to 32 samples. We found no fast radio bursts above a threshold of approximately 40 Jy/sqrt(ms). We thank the CSIRO staff for supporting these observations. [1] Bannister et al. 2017, ApJL, 841, 12 -- Keith Bannister //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21672 SUBJECT: LIGO/Virgo G298048: INTEGRAL pointed follow-up observations DATE: 17/08/24 09:03:02 GMT FROM: Volodymyr Savchenko at APC,Paris V. Savchenko (ISDC, University of Geneva, CH) C. Ferrigno, E. Bozzo ((ISDC, University of Geneva, CH), E. Kuulkers (ESTEC/ESA, The Netherlands), S. Mereghetti (IASF-Milano, Italy), T. J.-L. Courvoisier (ISDC, University of Geneva, CH) J. Chenevez, S. Brandt (DTU, Denmark) R. Diehl (MPE-Garching, Germany) L. Hanlon (UCD, Ireland) P. Laurent, D. Gotz (APC, Saclay/CEA, France) J.P. Roques, E. Jourdain (IRAP, France) P. Ubertini, A. Bazzano, J. Rodi (IAPS-Roma, Italy) A. Lutovinov, R. Sunyaev (IKI, Russia) INTEGRAL is an observatory with multiple instruments: a gamma-ray spectrometer (20 keV - 8 MeV, SPI), an imager (15 keV - 2 MeV, IBIS), an X-ray monitor (3 - 25 keV, JEM-X), and an optical monitor (V band, OMC). Our group requested and obtained follow-up observations of the LIGO/Virgo candidate NS merger G298048 (GCN 21505, 21506). The initial observation was centered on the best Fermi/GBM localization, RA=176.8, Dec=-39.8 (GCN 21509), and was carried out from 2017-08-18 08:17:51 to 2017-08-18 12:36:11 for a total observing time of 14.8 ks. It covered 72% of the Fermi/GBM localization probability but only a negligible fraction of the current LIGO/Virgo localization. We do not detect any new sources in the complete IBIS/ISGRI (20-80 keV and 80 - 300 keV) and JEM-X (3-10 keV, 10 - 25 keV) mosaicked images, with a best sensitivity of 7.9 mCrab (1.2e-7 erg/cm2/s) in the 20 - 80 keV energy range. The main part of the INTEGRAL follow-up observation was centered on the candidate optical counterpart SSS17a (RA=13:09:48.089 Dec=-23:22:53.35; GCN 21529). This observation spanned from 2017-08-18 12:45:10 to 2017-08-23 04:07:47 (starting about 24 hours after the LIGO/Virgo event), with a maximum on-source time of about 330 ks (depending on the instrument). SSS17a was in IBIS and SPI FoV in each of the dithered single pointing that make up an INTEGRAL observations; whilst it was in the JEM-X FoV only a fraction of the time. We investigated the complete observation mosaics of ISGRI, SPI, and JEM-X data. INTEGRAL provides the most stringent constraint on any possible emission associated with SSS17a above 80 keV. We do not detect the source in any energy ranges of any of the INTEGRAL instruments, and set the following 3-sigma upper bounds for an average flux of a source at the position of SSS17a: JEM-X: 3-10 keV: 1.2 mCrab (1.9e-11 erg/cm2/s ) 10-25 keV: 0.64 mCrab (7e-12 erg/cm2/s ) ISGRI: 20-80 keV: 2.6 mCrab (3.8e-11 erg/cm2/s) 80-300 keV: 6.2 mCrab (7.1e-11 erg/cm2/s) 300-500 keV: 291.6 mCrab (1e-9 erg/cm2/s) SPI: 20 - 80 keV: 7.2 mCrab (1.1e-10 erg/cm2/s) 80 - 300 keV: 24 mCrab (2.8e-10 erg/cm2/s) 300 - 500 keV: 175 mCrab (6.1e-10 erg/cm2/s) 500 - 1000 keV: 770 mCrab (3.1e-9 erg/cm2/s) 1 MeV - 2 MeV: 1.0 Crab (3.3e-9 erg/cm2/s) We have also searched for isolated line-like features in ISGRI and SPI data, and preliminary analysis did not identify any such features. Further analysis is ongoing. IBIS, SPI, and JEM-X observed more than 97% of the of LIGO localization in the combined observation mosaic. We searched IBIS/ISGRI and JEM-X data for any new point source in the whole 90% LIGO/Virgo localization region, and did not find any. The sensitivity depends on the location, with the best value close to that computed for SSS17a. Continuous observation provided by INTEGRAL allows us to perform an exhaustive search for any short (magnetar-like) or long bursts from SSS17a. We build IBIS/ISGRI light-curves in 2 energy ranges: 20-80 keV, 80-300 keV, on 100 ms, 1 s, 10 s, and 100 s time scales. The lightcurves span from 2017-08-18T12:45:10 to 2017-08-23T04:07:47 with a coverage fraction of 80%. We did not find any deviations from the background, and set a 3-sigma upper limit on any possible 1-s long burst flux of 1.0 Crab (1.4e-8 erg/cm2/s) in 20-80 keV, and 6.8 Crab (7.8e-8 erg/cm2/s) in 80-300 keV. We also inspected the JEM-X (3-25 keV) light curves at 10 s time scale, and did not find any significant fluctuations apart from sporadic particle contaminations). The corresponding upper limit in 3-25 keV is 0.4 Crab (1.3e-8 erg/cm2/s). Analysis of the PICsIT spectral-timing data with 100 s time resolution in four energy bands spanning 208-2600 keV did not reveal any significant variability associated with SSS17a during revolutions 1852 and 1853. During these observation INTEGRAL/IBAS system identified two weak triggers (at 2017-08-22 21:05:59 and 2017-08-22 05:48:21). The localization of these events is not compatible with SSS17a. We consider these events to be noise associated with moderate solar activity. Unfortunately, the optical camera on-board INTEGRAL, OMC, was unable to disentangle SSS17a from the host galaxy NGC4993. We acknowledge the exceptionally efficient support by the teams at ESAC and ESOC for the scheduling of this follow-up observation. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21674 SUBJECT: LIGO/Virgo G298048: H.E.S.S. very-high energy gamma-ray follow-up DATE: 17/08/24 10:35:02 GMT FROM: Fabian Schussler at HESS Observatory M. de Naurois on behalf of the H.E.S.S. collaboration The H.E.S.S. array of imaging atmospheric Cherenkov telescopes was used to carry out follow-up observations of the GW trigger G298048 (GCN #21509) and monitoring of the possible counterpart SSS17a/DLT17ck (Coulter et al. GCN #21529; Yang et al., GCN #21531). H.E.S.S. observations started August 17 at 18:00 UTC with three pointings derived from the HLV-Bayestar map (GCN #21513) without assumptions on the orientation of the system and cross correlated in three dimensions with the GLADE catalog [1]. The first of these pointings covered the region of NGC 4993 and the potential EM counterpart SSS17a/DLT17ck. We continued to monitor the region around SSS17a/DLT17ck during the following nights until the location moved outside the H.E.S.S. visiblity window. The last pointing was taken August 22, 18:00 UTC. Each of our observations has a sensitivity of about 20% of the flux from the Crab nebula at 5 sigma. A preliminary analysis with an energy threshold of about 500GeV did not reveal significant gamma-ray emission in any of the datasets. Further analyses of the data are on-going. H.E.S.S. is an array of five imaging atmospheric Cherenkov telescopes for the detection of very-high-energy gamma-ray sources and is located in the Khomas Highlands in Namibia. It was constructed and is operated by researchers from Armenia, Australia, Austria, the Czech Republic, France, Germany, Ireland, Netherlands, Japan, Poland, South Africa, Sweden, UK, and the host country, Namibia. For more details see https://www.mpi-hd.mpg.de/hfm/HESS/ [1] GLADE website: http://aquarius.elte.hu/glade/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21676 SUBJECT: LIGO/Virgo G298048: LOFAR follow-up DATE: 17/08/24 13:35:06 GMT FROM: Peter Jonker at SRON/RU J.W. Broderick (ASTRON), A. Rowlinson (UvA, ASTRON), P.G. Jonker (SRON, RU), R.P. Fender (Oxford), R.A.M.J. Wijers (UvA), B.W. Stappers (Manchester), S. ter Veen (ASTRON), S. Nissanke (RU) and A. Shulevski (ASTRON) report on behalf of the LOFAR Transients Key Science Project On 2017 August 22, we conducted a LOFAR follow-up observation of the Advanced LIGO/Virgo trigger G298048 with the ILT (International Low-Frequency Array [LOFAR] Telescope). This is a highly experimental observation to assess whether images of sufficient quality can be obtained at very low elevations. The observation began at 14:05:00 UTC, near transit, with any useable data likely only within the first hour. We placed two beams on the most northerly part of the probability distribution, as determined from the preliminary LALInference map. The bandwidth for each beam is 47.5 MHz, spread over the frequency range 120-187 MHz. The beam centres (RA/Dec), in degrees, are as follows: 1) 192.4167 -15.8333 2) 193.1875 -17.0000 where the field of view per beam is 11.35 deg^2 at 150 MHz. Analysis is ongoing, with the possibility of further observations if this test run is deemed to have been successful. We thank the ASTRON Radio Observatory for rapidly scheduling the observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21677 SUBJECT: LIGO/VIRGO G298048: AAT/AAO spectroscopic observations of the GW counterpart candidate SSS17a/DLT17ck DATE: 17/08/24 15:31:25 GMT FROM: Igor Andreoni at Swinburne U of Tech I. Andreoni (Swinburne), J. Cooke (Swinburne) on behalf of OzGrav and C. Lidman, E. Elmer and T. Farrell (AAO) We performed spectroscopic observations of the GW counterpart candidate SSS17a/DLT17ck (Coulter et al., LVC GCN 21529; Allam et al., LVC GCN 21530; Sheng Yang et al., LVC GCN 21531) with the AAOmega spectrograph at the 4m Anglo-Australian Telescope. The AAOmega spectrograph covers a wavelength range 3700-8800 AA with a resolution R=1700. We obtained 4 usable exposures of 600s each, starting at 2017-08-24.037 UT. A preliminary analysis shows a red, largely featureless spectrum with no obvious features other than host galaxy absorption lines. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21680 SUBJECT: LIGO/Virgo G298048: LWA radio observations DATE: 17/08/24 16:08:17 GMT FROM: Christopher League at FRBSG T. Callister (Caltech), J. Dowell (U New Mexico), J. Kanner (Caltech), M. Kavic (LIU Brooklyn), C. League (LIU Brooklyn), P. Shawhan (U Maryland), J. Simonetti (Virginia Tech), G. Taylor (U New Mexico), J. Tsai, C. Yancey (U Maryland) The Long Wavelength Array (LWA1, located west of Socorro, New Mexico) [S.W. Ellingson, et al. http://lanl.arxiv.org/abs/1204.4816] made observations on June 17 following the LIGO trigger G298048. The first observation began at 2017-08-17 13:09:51 UTC (28 minutes after the trigger) and ran for approximately 1.1 hours. All observations were centered at frequencies 25.85 MHz and 45.45 MHz, each with a bandwidth of 19.6 MHz. The FWHM is 15.499 degrees at 25.85 MHz, and 6.648 degrees at 45.45 MHz. The beam centers for the first observation were: Beam 1: RA 2.391h, Dec 41.810deg; Beam 2: RA 2.431h, Dec 46.572deg; Beam 3: RA 2.803h, Dec 44.202deg; and Beam 4: RA 2.660h, Dec 50.480deg. These were chosen to observe the maximum of the LIGO skymap available with the initial notice. The next observation, using an updated skymap, began at 2017-08-17 19:15:00 UTC (6.6 hours after the trigger) and ran for 4 hours. The beam centers for the second observation were Beam 1: RA 12.814h, Dec -13.862deg; Beam 2: RA 12.955h, Dec -17.896deg; Beam 3: RA 13.096h, Dec -22.024deg; and Beam 4: RA 11.786h, Dec -39.840deg. These coordinates include the position of the observed transient, as reported by D.A. Coulter, et al., [GCN 21529], as well as nearby regions. We plan to continue follow-up observations at the second set of coordinates over the next few weeks. Data analysis is proceeding. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21681 SUBJECT: LIGO/Virgo G298048: MUSE Integral Field Observations DATE: 17/08/24 19:28:30 GMT FROM: Andrew Levan at GOTO A.J. Levan, J.D. Lyman, D.T.H. Steeghs (U. Warwick), N.R. Tanvir (U. Leicester), J. Hjorth (Dark Cosmology Centre) report on behalf of a larger collaboration: "We observed the candidate counterpart and host galaxy (NGC 4993) of LIGO/Virgo G298048 (LSC GCN 21509) with the ESO VLT and the MUSE Integral Field Unit, starting at 2018 August 18.99. MUSE has a 1’ field of view, and a spectral range from 4650-9300A. Both the host galaxy and transient are clearly visible. The bulk spectrum of the transient is comparable to others reported at the same epoch (Lyman et al. GCN 21582, Nicholl et al. GCN 21585, D’Elia et al. GCN 21592). The galaxy is dominated by a spheroidal component, but weak spiral arms can be seen in emission lines extending both north and south from the centre of the galaxy. They do not reach the location of the transient, and no underlying star formation in the form of emission lines is evident in the vicinity of the transient source. Further analysis is ongoing. We thank the staff at Paranal for their excellent assistance in performing the observations." //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21682 SUBJECT: LIGO/Virgo G298048: Gemini-South Imaging and Spectroscopy DATE: 17/08/24 19:31:19 GMT FROM: Eleonora Troja at GSFC/Swift E. Troja (UMD/GSFC), A. Watson (UNAM), S. Covino (INAF), W. H. Lee (UNAM), N. Butler (ASU), J. Becerra-Gonzalez (UMD/GSFC), A. Lien (UMBC), T. Sakamoto (AGU), and P. D'Avanzo (INAF) and L. P. Singer (NASA/GSFC), C. Fremling (Caltech), and M. M. Kasliwal (Caltech) on behalf of the GROWTH (Global Relay of Observatories Watching Transients Happen) collaboration report: We observed the field of the transient SSS17a in NGC 4993 (Coulter et al. 2017; GCN 21529) with the Flamingos-2 (F2) instrument and the Gemini Multi-Object Spectrograph (GMOS) mounted on the Gemini- South 8-m telescope starting on 2017 Aug 20.98 UT, ~3.5 days after LIGO/Virgo trigger G298048 (LVC GCN Circ. 21509, 21513). Imaging observations were carried out in the g, r, i, z, J, H and K filters. The source is detected in all bands with a preliminary magnitude J~17.2. We also obtained a pair of 1200s GMOS spectra with the R400 and the B600 gratings. We do not detect any significant emission or absorption lines over the red featureless continuum. We thank the Gemini staff, particularly Hwihyun Kim, Ricardo Salinas, and Laura Ferrarese for their support of these operations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21683 SUBJECT: LIGO/Virgo G298048: HAWC follow-up DATE: 17/08/24 19:35:19 GMT FROM: Israel Martinez-Castellanos at UMD/HAWC I. Martinez-Castellanos (University of Maryland, College Park) and A.J. Smith (University of Maryland, College Park) on behalf of the HAWC Collaboration: HAWC Collaboration performed a follow-up of LIGO trigger G298048. At the time of the trigger no portion of the LV contour was visible to HAWC, so no prompt follow-up was possible. About 9hrs after the trigger the LV region transited through the HAWC FOV (95% of the probability was covered), albeit with a large zenith angle, which limits the sensitivity of our observations. There were no >5 sigma points observed during this transit. For a single transit, the 5 sigma sensitivity to a power law spectrum with a -2.5 index ranges from ~2e-11 >1TeV cm^-2 s^-1 (~3 Crab units) at dec=-12 to about 6 times higher at the edge of our FOV, dec=-25. At the point of the optical counterpart candidate SSS17a/DLT17ck (RA=13:09:48.09 DEC=-23:22:53.35) reported by Coulter et al. (LVC GCN 21529), Allam et al. (LVC GCN 21530), Yang et al. (LVC GCN 21531), Melandri et al. (LVC GCN 21532), we obtain an 95% confidence level upper limit for >1TeV assuming a -2.5 spectrum of 1.0e-10 cm^-2 s^-1. These observations were made on 2017-08-17 between 19:57 UT and 23:25 UT with culmination 9:00 hrs after the LV trigger. HAWC is a TeV gamma ray water Cherenkov array located in the state of Puebla, Mexico. It is sensitive to the energy range ~0.5-100TeV, and monitors 2/3 of the sky every day with an instantaneous field-of-view of ~2 sr. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21684 SUBJECT: LIGO/Virgo G298048: Near-infrared fading from Gemini-South DATE: 17/08/25 04:04:17 GMT FROM: Ryan Chornock at Ohio U R. Chornock (Ohio University) and E. Berger (Harvard) report on behalf of a larger collaboration: Further to our previous report (LVC GCN 21638), we have continued near-infrared observations of the optical counterpart (Coulter et al., LVC GCN 21529; Allam et al., LVC GCN 21530; Yang et al., LVC GCN 21531) to the LIGO/Virgo source G298048 (GCNs 21509, 21513) using FLAMINGOS2 on Gemini-South (PI: Chornock). Over the course of our initial observations, obtained during the first 4.5 days after the GW trigger, the H-band flux from the near-infrared source was not strongly variable. However, in H-band acquisition images obtained tonight (20170824 at 23:47 UT, t~7.5 d after the GW trigger), the NIR counterpart appears substantially fainter (by >1 magnitude) compared to our previous observations three nights earlier. A phase of more rapid NIR fading may have begun. We thank the entire Gemini-South staff, but particularly H. Kim, G. Diaz, J. Chavez, P. Candia, and the director, Laura Ferrarese, for their support of these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21685 SUBJECT: LIGO/Virgo G298048: Subaru HSC z-band imaging of the OT candidate SSS17a DATE: 17/08/25 07:38:17 GMT FROM: Michitoshi Yoshida at J-GEM Yoshida, M., Tanaka, M. (NAOJ), Utsumi, Y. (Hiroshima Univ.), Tominaga, N. (Konan Univ.), Ohsawa, R., Motohara, K. (Univ. of Tokyo), Terai, T., Nakata, F., Lee, C. H., Furusawa, H., Koshida, S. (NAOJ), Ohta, K. (Kyoto Univ.), Kawabata K. S. (Hiroshima Univ.), Morokuma, T., Yasuda, N. (Univ. of Tokyo), Kawai, N. (Tokyo Tech.), and Asakura, Y. (Nagoya Univ.) on behalf of the J-GEM collaboration We have performed z-band imaging observations of the OT candidate of G298048, SSS17a (Coulter et al., GCN 21529) with Hyper Suprime-Cam attached to the Subaru telescope on August 25.2 2017 UT. We found that the z-band magnitude of the source was significantly fainter compared to our previous observations on August 19.2 2017 UT (Yoshida et al. GCN 21586; Tominaga et al. GCN 21595). Further analysis is ongoing. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21686 SUBJECT: LIGO/Virgo G298048: Pierre Auger Observatory neutrino follow-up DATE: 17/08/25 08:13:23 GMT FROM: Jaime Alvarez-Muniz at Pierre Auger Observatory J. Alvarez-Muniz, F. Pedreira, E. Zas (Univ. Santiago de Compostela, Spain), K. H. Kampert & M. Schimp (Bergische Universitat, Wuppertal, Germany) on behalf of the Pierre Auger Collaboration. In response to: LIGO/Virgo GW trigger G298048 (GCN #21505 and #21509 ,T0=2017-08-17 at 12:41:04.527 UTC) We searched for Ultra-High-Energy (UHE) neutrinos with energies above ~ 1e17 eV in data collected with the Surface Detector (SD) of the Pierre Auger Observatory in a [-500,500] second interval about the LIGO-Virgo trigger G298048 as well as 1 day after it. The field of view (fov) where the SD of Auger is sensitive to UHE neutrinos (corresponding to inclined directions with respect to the vertical relative to the ground) was FULLY COINCIDENT with the LIGO+Virgo 90% localization region (GCN #21513 bayestar-HLV.fits.gz) at the time T0 of the merger alert as well as with the optical counterpart detected by the Swope telescope (GCN #21529). Also the 90% CL Fermi GBM trigger 170817.529 contour (GCN #21506) at the trigger time was largely overlapping with the Auger fov. NO events survived the cuts applied to reject the background due to UHE Cosmic Rays i.e. NO neutrino candidates were detected. ------- The Pierre Auger Observatory is an UHE Cosmic Ray detector located in the Mendoza Province in Argentina. It consists of an array of Water Cherenkov detectors spread over a total surface of 3000 km^2 arranged in a triangular grid of 1.5 km side as well as Fluorescence telescopes and other systems (see 10.1016/j.nima.2015.06.058 for more information). For neutrino searches from GW events with Auger, please refer to: https://journals.aps.org/prd/pdf/10.1103/PhysRevD.94.122007 //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21687 SUBJECT: LIGO/Virgo G298048: MASTER Global-Net early optical observations and the Possible KiloNova SSS17a in NGC 4993 photometry and merging rate DATE: 17/08/25 08:48:24 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs V.M.Lipunov, E. Gorbovskoy, V.G.Kornilov, N.Tyurina, V.Shumkov, D.Kuvshinov, P.Balanutsa, O.Gress, A.Kuznetsov, M.I.Panchenko, A.V.Krylov, I.Gorbunov Lomonosov Moscow State University, Sternberg Astronomical Institute R.Podesta, C.Lopez, F.Podesta Observatorio Astronomico Felix Aguilar (OAFA) , National University of San Juan, Argentina H.Levato, C.Saffe Instituto de Ciencias Astronomicas,de la Tierra y del Espacio (ICATE), San Juan, Argentina D.Buckley, S.Potter, M.Kotze, South African Astronomical Observatory N.M. Budnev, O. Gress, K. Ivanov, S.Yazev Irkutsk State University V.Yurkov, Yu.Sergienko, A.Gabovich Blagoveschensk Educational State University, Blagoveschensk R. Rebolo, M. Serra-Ricart, G. Israelian, N.Lodiu The Instituto de Astrofisica de Canarias A. Tlatov, V.Sennik Kislovodsk Solar Station of the Pulkovo Observatory MASTER Global Robotic Net (http:/ / observ.pereplet.ru/ ) consists of a new generation of fast robotic telescopes that installed on different continents during recent years. MASTER-II are twin 40 cm wide field (2x4 square degrees, 1 pixel = 2.0 arcsec) optical robotic telescopes located in the following observatories: MASTER-Amur (far east of Russia, Blagoveshchensk), MASTER-Tunka (Russia, Baykal lake), MASTER-Kislovodsk, MASTER-Tavrida (Russia), MASTER-SAAO (South Africa), MASTER-IAC (Spain, Canarias), and MASTER-OAFA (Argentina, MASTER I yet). MASTER observatories are equipped with their own identical photometers and are controlled by identical software (Lipunov et al., "MASTER Global Robotic Net", Advances in Astronomy, 2010, 30L). The identical equipment gives us the possibility of having up to 24 continuous hours observations of optical counterparts of GRBs in identical photometric systems. Therefore, combining photometric data for different GRBs observed from different parts of the MASTER Net is a well-justified astronomical process (see last result in Troya, Lipunov, Mundel et al., Nature, 2017, vol.547,425-427) Taking into account the large field of view of the MASTER II telescopes (8 square degrees), we can use a large number (1000 - 5,000) of reference stars for reduction. As a result, the photometric errors of large catalogs, Tycho II and USNO-B1, shouldbe leveled out. Global MASTER-Net started to observe LIGO/Virgo G298048 error field at 2017-08-17 17:06:47 UT. MASTER-SAAO (MASTER II robotic telescope at South Africa Astronomical Observatory, Sutherland) automaticaly have imaged the initial BAYESTAR error field received by socket connection (LVC GCN 21505) including common region with Fermi GBM error box (Connaughton et al., LVC GCN 21506) immediatelly after sunset at 2017-08-17 17:06:47 = 2017-08-17.71304 (JD = 2457983.21304398) i.e. 15943 sec after LVC trigger time (12:41:04 UT) . The coaadded (3x180sec) first unfiltered images limit is 19.8. This image included ICECube candidate N4 (Bartos et al LVC GCN 21511). No OTs found in this error box. After that MASTER-SAAO telescope continue to image Fermi and LVC initial common error field and all Ice Cube candidates. The unfiltered limits and fields one can find at GraceDB. Cover map is available at http://master.sai.msu.ru/static//ligo/db/G298048/151A//img/MASTER.G298048.180.24.gif No OTs found at this observations. The Possible KiloNova SSS17a in NGC 4993 (Coulter et al., LVC GCN 21529) is not covering by MASTER-SAAO at 17 Aug 2017. MASTER-OAFA (MASTER I robotic telescope with FOV = 6 square degrees; at Argentina, Observatorio Astronomico Felix Aguilar (OAFA), National University of San Juan,) have imaged the new BAYESTAR-HLV localization map of LIGO/Virgo G298048 (GCN 21513) starting 2017-08-17 22:54:18 = 2017-08-17.954375 from first field (6 square degrees): RA, DEC = 12h 59m 00.00s -19d 59m 38.00s Unforunatelly the first telescope image not include sss17a. But fortunally there are two MASTER Very Wide Field cameras (FOV = 2x380 square degrees, 22 arcsec in pixel, see Lipunov et al., 2010, MASTER Robotic Net, Advances in Astronomy, vol. 2010, pp. 1-7) at same mount. As the results we have large seria ("video") MASTER VWF cameras images exposition and without time gap of the all LIGO/Virgo G298048 error box include the NGC 4993 galaxy. We see NGC 4993 galaxy on coadded images. After the images substraction with refernce very wide field camera images we see some excess (see Table 1) at NGC 4993 position with flux corresponded to ~15.3 mag. Starting from 2017-08-17 22:58:48 UT = 2017-08-17 22:58:48 MASTER-OAFA have imaged new BAYESTAR-HLV localization map of LIGO/Virgo G298048 (GCN 21513) with unfiltered images (150 sec exposition) limit 19-20 magnitudes. The coadded images limit grows to 20.5. At 2017-08-17 23:59:54 UT i.e. 11 h 18m 50 sec after LVC trigger time MASTER-OAFA robotic telescope independently from any optical information take second image with NGC 4993 galaxy where Possible KiloNova SSS17a was published late Coulter et al., LVC GCN 21529, Allam et al. (LVC GCN 21530), Yang et al. (LVC GCN 21531), Melandri et al. (LVC GCN 21532), Lipunov et al., (LVC GCN 21546), Chen et al. (LVC GCN 21608). On the next 3 days both southern MASTER robotic telescopes at SAAO and OAFA was done (and continue now) B,R, Unfiltered monitoring Possible KiloNova SSS17a at NGC 4993 galaxy. The covering video map at first day is available at http://master.sai.msu.ru/static//ligo/db/G298048/151//img/MASTER.G298048.180.24.gif The photometry of sss17a listed at Table I. This photometry made by substracted images and free from galaxy background. TableI. MASTER Global Robotic Net the sss17a photometry ----------------------------------------------------------------------- Date UT T-Ttrig Exp Filt Mag Err Lim Instr SITE start Kilosec sec 2017-08-17 22:54:18 36.794 225x5 V 15.3* 0.5 15.5 MASTER VWFC OAFA 2017-08-17 23:59:54 40.730 180 W 17.7 0.2 19.5 MASTER I OAFA 2017-08-18 00:19:05 41.881 180 W 17.3 0.2 19.3 MASTER I OAFA 2017-08-18 17:06:55 102.352 6x180 W 17.5 0.2 20.0 MASTER II SAAO 2017-08-18 17:17:33 102.989 3x180 R 17.2 0.2 19.8 MASTER II SAAO 2017-08-18 17:34:02 103.979 3x180 B 18.5 0.1 19.5 MASTER II SAAO 2017-08-19 17:06:57 188.753 3x180 W 18.6 0.2 20.0 MASTER II SAAO 2017-08-19 17:53:34 191.550 3x180 R 18.2 0.3 19.8 MASTER II SAAO 2017-08-19 18:04:32 192.208 3x180 B ---- --- 19.5 MASTER II SAAO 2017-08-19 23:13:20 210.736 10x180 W 19.0 0.2 20.7 MASTER I OAFA 2017-08-20 17:04:36 275.012 3x180 W >19.3 --- 20.0 MASTER II SAAO 2017-08-20 17:25:56 276.292 3x180 R >18.8 --- 19.5 MASTER II SAAO 2017-08-20 17:36:32 276.928 3x180 B >19.7 --- 20.0 MASTER II SAAO 2017-08-21 00:26:31 301.527 10x180 W >20.0 --- 20.7 MASTER I OAFA 2017-08-21 17:08:14 361.630 3x180 W >19.3 --- 20.0 MASTER II SAAO 2017-08-21 18:06:12 365.108 3x180 R >18.8 --- 19.5 MASTER II SAAO 2017-08-21 19:20:23 369.559 3x180 B >18.7 --- 19.0 MASTER II SAAO ----------------------------------------------------------------------- * This is a photometry of some faint excess on substracted image. It is possible to be a image substraction noice. Ttrig - LVC trigger Time T - is the exposition start time W - unfiltered VWFC - Very Wide Field Camera Table 2. Start and midle times. --------------------------------------------------------- Date UT JD UT start start midle 2017-08-17 22:54:18 2457983.454 23:03:40 2017-08-17 23:59:54 2457983.4999 00:01:24 2017-08-18 00:19:05 2457983.513 00:20:35 2017-08-18 17:06:55 2457984.217 17:11:57 2017-08-18 17:17:33 2457984.226 17:25:27 2017-08-18 17:43:02 2457984.236 17:39:14 2017-08-19 17:06:57 2457985.213 17:11:52 2017-08-19 17:53:34 2457985.246 17:58:29 2017-08-19 18:04:32 2457985.253 18:09:27 2017-08-19 23:13:20 2457985.468 23:30:50 2017-08-20 17:04:36 2457986.212 17:09:31 2017-08-20 17:25:56 2457986.226 17:30:51 2017-08-20 17:36:32 2457986.234 17:41:27 2017-08-21 00:26:31 2457986.518 00:44:01 2017-08-21 17:08:14 2457987.214 17:13:09 2017-08-21 18:06:12 2457987.254 18:11:07 2017-08-21 19:20:23 2457987.306 19:25:18 --------------------------------------------------- There are MASTER-NET 126 arhival images of the NGC 4993 galaxy since 2015-01-17 00:45:46 till 2017-05-02 22:17:04 . No optical sss17a activity was found. The MASTER arhival images table is available at http://master.sai.msu.ru/static/MASTER_G298048_PREDISCOVERY1.txt . As the discussion about physical nature GW 170817/G298048 (Lipunov, LVC GCN 21621; Nichol etal., LVC GCN 21585, LVC GCN 21592; D'Elia et al.,LVC GCN 21592 ) I (Vladimir Lipunov) would like to point that distance of the binary NS merging ~ 40 Mpc is in good agreement with predicted merging rate inside local super cluster (Lipunov, Postnov & Prokhorov, 1987, A&A, vol.176, L1-L4.). See fig. 1 which is vailable at http://master.sai.msu.ru/static/LPP1987_fig1.jpg . There was predicted 1 merging NS+NS per year for 20 Mpc radius volume(e-case, see capture). This means, that for 40 Mpc predicted ~ 10 per year! This message can be citted. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21695 SUBJECT: LIGO/Virgo G297595: INTEGRAL pointed follow-up observations DATE: 17/08/25 14:33:57 GMT FROM: Volodymyr Savchenko at APC,Paris V. Savchenko (ISDC, University of Geneva, CH) on behalf of the INTEGRAL group: C. Ferrigno, E. Bozzo ((ISDC, University of Geneva, CH), E. Kuulkers (ESTEC/ESA, The Netherlands), S. Mereghetti (IASF-Milano, Italy), T. J.-L. Courvoisier (ISDC, University of Geneva, CH) J. Chenevez, S. Brandt (DTU - Denmark) R. Diehl (MPE-Garching, Germany) L. Hanlon (UCD, Ireland) P. Laurent (APC, Saclay/CEA, France), D. Gotz (DRF/Irfu/DAp Saclay/CEA) J.P. Roques, E. Jourdain (IRAP, France) P. Ubertini, A. Bazzano, J. Rodi (IAPS-Roma, Italy) A. Lutovinov, R. Sunyaev (IKI, Russia) INTEGRAL is an observatory with multiple instruments: a gamma-ray spectrometer (20 keV -4 MeV, SPI), an imager (15 keV - 2 MeV, IBIS), an X-ray monitor (3-25 keV, JEM-X), and an optical monitor (V band, OMC). Our group requested and obtained pointed follow-up observations of the LIGO/Virgo candidate BBH merger G297595 (GCN 21474). The INTEGRAL follow-up observation was centered on RA=41.07 Dec=-45.49, close to the peak of the LIGO/Virgo localization probability, taking into account observational constrains. This observation spanned from 2017-08-16 at 10:04 to 2017-08-17 at 18:19 (starting about 47 hours after the LIGO/Virgo event), with a maximum on-source time of 97.5 ks (depending on the instrument). IBIS and SPI observed more than 92% of the of LIGO/Virgo localization in the combined observation mosaic. JEM-X covered about 79%, owing to its smaller Field of View. INTEGRAL provides the most stringent constraint on any possible emission associated with G297595, above 80 keV. We searched IBIS/ISGRI and JEM-X data for new point sources in the whole 90% LIGO/Virgo localization region, and did not find any. We set the following 3-sigma upper limits for the average flux: JEM-X: 3-10 keV: 2.0 mCrab (3.2e-11 erg/cm2/s ) 10-25 keV: 1.0 mCrab (1.1e-11 erg/cm2/s ) ISGRI: 20-80 keV: 3.3 mCrab (4.9e-11 erg/cm2/s) 80-300 keV: 13.1 mCrab (1.5e-10 erg/cm2/s) In the case of ISGRI (JEM-X), 82% (59%) of the of LIGO/Virgo localization is covered with sensitivity no more than factor two worse than the best. During these observation online INTEGRAL/IBAS system identified several weak triggers. After offline inspection, we consider these triggers unrelated noise. INTEGRAL/IBAS online search in the SPI-ACS identified a bright GRB170816A on 2017-08-16 at 14:22:58. The location of this GRB is inconsistent with the LIGO/Virgo 90% localization (GCN 21504, 21517). Finally, the BNS merger G298048 (GCN 21509, 21513) candidate counterpart (GRB 170817A, GCN 21506, 21520) was detected in the INTEGRAL data during this observation, as reported in GCN 21507. We have also inspected PICsIT spectral-timing data (200 - 2600 keV) and did not find any evidence for significant variability. Further analysis is ongoing. We acknowledge the essential support by the teams at ESAC and ESOC for the scheduling of this follow-up observation. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21703 SUBJECT: LIGO/VIRGO G298048: INAF VST-ESO PARANAL observations of NGC4993 DATE: 17/08/25 22:15:33 GMT FROM: Aniello Grado at INAF-OAC A. Grado (INAF-OAC), F. Getman (INAF-OAC), L. Limatola (INAF-OAC), E. Cappellaro (INAF-OAPD), M. Branchesi (GSSI), S. Covino (INAF-OAB), P. D'Avanzo (INAF-OAB), A. Melandri (INAF-OAB), L. Amati (INAF-IASF Bo), L. A. Antonelli, (INAF-OAR), S. Ascenzi (INAF-OAR), S. Benetti (INAF-OAPD), M.T. Botticella (INAF-OAC), S. Campana (INAF-OAB), V. D'Elia (INAF-ASDC), D. Fugazza, M. Lisi (INAF-OAR), G. Greco (Urbino University/INFN Firenze), L. Nicastro (INAF-IASF Bo), E. Palazzi (INAF-IAFS Bo), E. Pian (INAF-IASF Bo), S. Piranomonte (INAF-OAR), L. Pulone (INAF-OAR), A. Rossi (INAF-IASF Bo), P. Schipani (INAF-OAC), G. Stratta (Urbino University/INFN Firenze), G. Tagliaferri (INAF-OAB), V. Testa (INAF-OAR), L . Tomasella (INAF-OAPD), S. Yang (INAF-OAPD), E. Brocato (INAF-OAR) on behalf of GRavitational Wave Inaf TeAm report: Observations of 1 square degrees of the skymap of the Advanced LIGO and Virgo trigger G298048 (LVC GCN Circ. 21509, 21513) were performed with the VLT Survey Telescope (VST - Proposal ID ESO 099.D-0191) at ESO-Paranal equipped with OMEGACAM (FOV=1 square degree). The observations cover the galaxy NGC4993. The images were acquired with the g_SDSS, r_SDSS, i_SDSS, z_SDSS filters for a total exposure of 200s in each filter. The observations started at 2017-08-22T 23:09:27.845 UTC and finished at 2017-08-23T 23:45:38.546 UTC. The optical counterpart at RA=13:09:48.09 DEC=-23:22:53.35 reported by Coulter et al. (LVC GCN 21529), Allam et al. (LVC GCN 21530), Yang et al. (LVC GCN 21531), Melandri et al. (LVC GCN 21532) and several others authors is visible in the gri filters with AB magnitudes of 23.3, 22.4 and 21.3 respectively, while is not visible in the z band. Automatic data reduction with the VSTTube pipeline (Grado et al. 2012 Mem.SAIt 19, 362 ) was completed. We acknowledge excellent support from the ESO User Support Department, in particular G. Beccari, and from ESO observing staff in Paranal. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21708 SUBJECT: LIGO/Virgo G298048: uGMRT Follow-up of SSS17a at 400 MHz and 1.4 GHz DATE: 17/08/26 01:23:58 GMT FROM: Mansi M. Kasliwal at Caltech K. De (Caltech), K. P. Mooley (Oxford), P. Chandra (NCRA), V. Bhalerao (IIT-B), A. Corsi (TTU), D. Kaplan (UWM), G. Hallinan (Caltech) and M. M. Kasliwal (Caltech) report on behalf of the GROWTH (Global Relay of Observatories Watching Transients Happen) collaboration We report on continued follow-up observations of SSS17a (GCN 21529; Coulter et al.) with the upgraded Giant Metrewave Radio Telescope (uGMRT) following the first epoch at 610 MHz (GCN 21603; De et al.). Observations were carried out on UT 20 August 2017 08:00 at 400 MHz (200 MHz bandwidth) for an on-source time of ~ 1 hour and on UT 20 August 2017 11:00 at 1.4 GHz (400 MHz bandwidth) for an on-source time of ~ 2 hours. After a preliminary analysis, no emission is detected at the location of the optical transient at 1.4 GHz up to a 3 sigma upper limit of 100 microJy. The transient was also undetected at 400 MHz, although this observation was partially affected by RFI and the analysis is being improved. Further multi-frequency observations are planned. We thank the GMRT staff for prompt scheduling of these observations. The GMRT is run by the National Center for Radio Astrophysics of the Tata Institute of Fundamental Research. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21740 SUBJECT: LIGO/Virgo G298048: Further ATCA follow-up of SSS17a in NGC 4993 DATE: 17/08/29 03:49:22 GMT FROM: Tara Murphy at U of Sydney C. Lynch (University of Sydney), T. Murphy (University of Sydney), D. Kaplan (UWM), K. Bannister (CSIRO), D. Dobie (University of Sydney) on behalf of the VAST collaboration. Following Lynch et al. (LVC GCN 21670), we observed a third epoch of NGC 4993 with the Australia Telescope Compact Array at 8.5 and 10.5 GHz. Observations started at 2017-08-27 23:26:24.9 UT and ended at 2017-08-28 9:00:00 UT with approximately 2.3 hours of on-source time. We fit and subtracted a point-source at the optical position of NGC 4993 (13:09:47.71, -23:23:01.79; Skrutskie et al. 2003, 2MASS Extended Source Catalog). From this we set a 3-sigma upper limit of 54 uJy and 39 uJy on radio emission from SSS17a at 8.5 and 10.5 GHz respectively. Subsequent epochs are planned. Thank you to CSIRO staff for supporting these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21744 SUBJECT: LIGO/Virgo G298048: Zadko Telescope 7 day observations of the OT candidate SSS17a/DLT17ck DATE: 17/08/29 08:29:39 GMT FROM: Eric Howell at U of Western Australia D. Coward (UWA), E. Howell (UWA), R. Laugier (ARTEMIS - CNRS/UCA/OCA), A. Klotz (IRAP - CNRS/UPS), M. Boer, (ARTEMIS - CNRS/UCA/OCA), I. Andreoni (Swinburne), J. Cook (Swinburne), D. Macpherson (UWA), J. Moore (UWA) and A. Burrell (UWA) report on behalf of OzGrav and TZAC (see acknowledgements below): We report 7 days of Zadko Telescope imaging of the transient SSS17a/DLT17ck in NGC4339 started on 2017-08-19 10:57 UT (t0+2 days). We use the stacked image of the night 201-08-26 (t0+9 days) as a mask to substract the light contribution from the galaxy NGC 4993 and synthesise one residual image for each nights observation. Photometry is performed using the star NOMAD-1 0666-0296321 for PSF fitting. The complete log of Zadko image analysis from t0+2 – t0+9 is: Tstart Tend r(AB) 1sigma 1.928 1.930 18.46 0.17 2.929 2.950 19.18 0.12 3.941 3.974 19.86 0.21 4.955 4.964 20.20 0.23 5.953 5.973 >20.6 6.958 6.978 >20.6 7.955 7.976 >20.6 Observations are compatible with a power law decay (alpha=-2) or with a exponential decay with a half time of 1.25 days. The Zadko Telescope is operated by the University of Western Australia (UWA), and was made possible by a philanthropic donation by James Zadko, to UWA. Zadko Telescope receives support from the ARC Centre of Excellence “OzGrav” for gravitational wave follow-up and discovery. The facility is managed by D.Coward (Director-UWA), E. Howell (UWA), J. Moore (UWA), A. Burrel (UWA), A. Greensky, J. Kennewell with collaborators I. Andreoni and J. Cook (Swinburne) This observation report was done in partnership with the LIGO follow-up collaboration TZAC, which is supported by M. Boer, A. Klotz, R. Laugier, K. Noysena //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21746 SUBJECT: LIGO/Virgo G298048: Konus-Wind observations DATE: 17/08/29 10:55:08 GMT FROM: Dmitry Svinkin at Ioffe Institute D. Svinkin, S. Golenetskii, R.Aptekar, D. Frederiks, P. Oleynik, M. Ulanov, A. Tsvetkova, A. Lysenko, A. Kozlova, and T. Cline, on behalf of the Konus-Wind team, report: Konus-Wind (KW) was observing the whole sky at the time of the LIGO/Virgo event G298048 (2017-08-17 12:41:04.446 UTC, hereafter T0; LIGO/Virgo Collaboration GCN Circ. 21509) coincident with Fermi GBM trigger 524666471 (Connaughton et al., GCN Circ. 21506, Goldstein et al., GCN Circ. 21528). Using waiting-mode data within the interval T0 +/- 100 s, we found no significant (> 4 sigma) excess over the background in both KW detectors on temporal scales from 2.944 s to 100 s. For the 2.944 s interval containing GBM trigger and the highest-probability localization region for the LIGO/Virgo G298048 (LVC, GCN Circ. 21513) we estimate an upper limit (90% conf.) on the 10 keV – 10 MeV fluence to 3.0x10^-7 erg/cm^2 for a burst lasting less than 2.944 s and having the spectrum reported by Goldstein et al. (an exponentially cut off power law, CPL, with alpha =-0.9 and Ep=128 keV). For a typical short GRB spectrum (CPL with alpha=-0.5 and Ep=500 keV), the limiting fluence is 6.9x10^-7 erg/cm^2 (10 keV – 10 MeV). All the quoted values are preliminary. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21747 SUBJECT: LIGO/Virgo G298048: ALMA observations DATE: 17/08/29 12:37:56 GMT FROM: Rhaana Starling at U.of Leicester S. Schulze (Weizmann Institute of Science), S. Kim (PUC Chile), S. Martin (JAO), F. E. Bauer (PUC Chile), M. Bremer (IRAM), S. Campana (INAF Brera), Z. Cano (IAA Granada), J. Corral-Santana (ESO Chile), P. D'Avanzo (INAF Brera), C. De Breuck (ESO), I. de Gregorio-Monsalvo (JAO), M. de Pasquale (Istanbul University), J. P. U. Fynbo (Dark Cosmology Centre), D. Garcia-Appadoo (JAO), D. Hartman (U. Clemson), J. Hjorth (Dark Cosmology Centre), P. Jakobsson (U. Iceland), D. A. Kann (IAA Granada), T. Kruehler (MPE Garching), R. Lekshmi (ARIES), A. J. Levan (U Warwick), A. Lundgren (JAO), D. Malesani (Dark Cosmology Centre), M. Michalowski (Adam Mickiewicz University), B. Milvang-Jensen (Dark Cosmology Centre), K. Misra (ARIES), S. R. Oates (U. Warwick), R. Sanchez-Ramirez (IAA Granada), M. Sparre (Heidelberg Institute for Theoretical Studies), R. L. C. Starling (U. Leicester), N. R. Tanvir (U. Leicester), C. C. Thoene (IAA Granada) and D. J. Watson (Dark Cosmology Centre) report: We have used the Atacama Large Millimeter/submillimeter Array, ALMA, to observe the field of LIGO/Virgo candidate G298048 (The LIGO Scientific Collaboration and the Virgo Collaboration GCN Circ. 21509) and GRB 170817A (Connaughton et al. GCN Circ. 21506; Svinkin et al. GCN Circ. 21515), centered on the position of the optical transient reported in Coulter et al. (GCN Circ. 21529). Observations were taken at four epochs: 2017-08-18, 2017-08-20, 2017-08-21 and 2017-08-25 and have been carried out in the B7 band centred at 338.5 GHz (central wavelength 0.89 mm). The field of view covered an area of 18.3 arcsec. Data processing is underway. We thank ALMA for their excellent support. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21750 SUBJECT: LIGO/Virgo G298048: ALMA upper limits on 98 GHz emission from SSS17a DATE: 17/08/29 14:55:15 GMT FROM: Peter K. G. Williams at Harvard P. K. G. Williams (Harvard), K. D. Alexander (Harvard), and E. Berger (Harvard) report on behalf of a larger collaboration: We observed the position of the optical counterpart SSS17a (Coulter et al., LVC 21529) with the Atacama Large Millimeter/submillimeter Array (ALMA) on 2017 August 19 UT and 2017 August 26 UT. Each observation lasted 20 minutes and was performed using ALMA's Band 3, with spectral windows of 4 GHz bandwidth centered at 91.5 and 103.5 GHz. We have analyzed the data using a custom CASA-based pipeline. At a mean frequency of 97.5 GHz, we detect no emission at the location of the optical transient to a combined 3-sigma limit of 50 microJy. We detect a source with a preliminary flux density of ~0.2 mJy at the location: RA = 13:09:47.696 dec = -23:23:02.31 with a positional uncertainty of ~0.04 arcsec. This is consistent with the optical position of the host galaxy and the position of the radio source reported by Alexander et al. (LVC 21545) and others. We thank the ALMA staff, especially Tony Remijan, for their excellent support. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21760 SUBJECT: LIGO/Virgo G298048: OVRO 40m telescope follow-up DATE: 17/08/30 03:23:28 GMT FROM: Mansi M. Kasliwal at Caltech T. J. Pearson and A. C. S. Readhead (Caltech) on behalf of the Owens Valley Radio Observatory. The KuPol receiver on the Owens Valley Radio Observatory 40m telescope is a dual-beam switched radiometer with a resolution ~ 3 arcmin operating in the 13-18 GHz band (http://www.astro.caltech.edu/ovroblazars/). We observed the candidate counterpart SSS17a and NGC 4993 at the following times (UTC): 2017-08-19T21:57:46 to 2017-08-20T01:38:52 2017-08-23T21:18:44 to 2017-08-24T00:10:30 On-off measurements of about 32s on-source integration were inerleaved with calibration observations, for a cadence of roughly 15 measurements per hour. In both periods there was no signal above our 3-sigma detection limit ~ 50 mJy in any individual on-off measurement. Further observations are planned, along with improved analysis to refine the upper limit. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21763 SUBJECT: LIGO/Virgo G298048: European VLBI Network (EVN) upper limit on 5 GHz compact emission from SSS17a DATE: 17/08/30 09:48:26 GMT FROM: Zsolt Paragi at Euro VLBI Zsolt Paragi (JIVE) Ivan Agudo (IAA Granada) Tao An (Shanghai Astronomical Observatory) Philippe Bacon (APC Université Paris Diderot) Rob Beswick (JBO-Manchester University) Carolina Casadio (MPIfR-Bonn) Eric Chassande-Mottin (APC Université Paris Diderot) Sándor Frey (Konkoly Observatory) Marcello Giroletti (IRA-INAF) Peter Jonker (SRON) Mark Kettenis (JIVE) Benito Marcote (JIVE) Arpad Szomoru (JIVE) Huib van Langevelde (JIVE) Jun Yang (Onsala Space Observatory) for the Euro VLBI team We observed SSS17a (Coulter et al. LVC GCN 21529) at 5 GHz with the European VLBI Network between 12:15—16:15 UT on 26 August 2017. Preliminary analysis shows no compact radio emission detectable on milliarcsecond angular scales above 160 microJy (~5 sigma) in a 1.6 x 1.6 arcsec region. Further observations are planned. The EVN is a joint facility of independent European, African, Asian, and North American radio astronomy institutes. Scientific results from data presented in this publication are derived from the following EVN project code: RP029. -- Zsolt Paragi Head of User Support Joint Institute for VLBI ERIC (JIVE) Web: http://www.jive.eu Oude Hoogeveensedijk 4 Phone: +31 (0)521-596-536 7991 PD Dwingeloo Mobile: +31 (0)629-034-718 the Netherlands Fax: +31 (0)521-596-539 //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21765 SUBJECT: LIGO/Virgo G298048: Discovery of X-ray emission from SSS17a in NGC4993 DATE: 17/08/30 12:07:12 GMT FROM: Eleonora Troja at GSFC/Swift E. Troja (UMD/GSFC), L. Piro (INAF/IAPS), T. Sakamoto (AGU), S. B. Cenko (NASA/GSFC), and A. Lien (UMBC/GSFC) report on behalf of a larger collaboration: We observed the field of SSS17a (Coulter et al., LVC GCN 21529) with the Chandra X-ray Observatory under our approved guest observer program (18500489; PI: E. Troja). Observations were carried out on 2017-08-26 (~9 days after the LVC trigger) for a total exposure of 50 ks. We detect the extended X-ray source visible in previous observations (Evans et al., LVC GCN 21612; Margutti et al., LVC GCN 21648) at a comparable flux level. In addition, we detect an X-ray source at the optical/IR transient position, approximately 10 arcsecond from the centroid of the extended X-ray emission. The probability to find an unrelated X-ray source within the small localization of the optical transient is negligible (<1E-5). Previous candidate kilonovae (e.g. GRB080513, Perley et al. 2009; GRB130603B; Tanvir et al. 2013) were associated to transient X-ray emission, although bright X-rays are not a basic prediction of this model. In our case, the properties of the X-ray emission and the overall spectral energy distribution appear different. The most likely explanation seems that the observed X-rays arise from the afterglow of GRB170817A (Connaughton et al., LVC GCN 21506; Savchenko et al., LVC GCN 21507), thus confirming the spatial association between the short GRB and SSS17a. A newborn spinning-down magnetar could power a long-lived and nearly constant X-ray emission (Zhang & Meszaros, 2001). However, the observed timescale and X-ray luminosity would imply unrealistic values of the initial spin period and magnetic field. The previous lack of detection from Chandra (Margutti et al., LVC GCN 21648) further disfavors this magnetar model. Other models (e.g. Metzger & Piro, 2014) also do not match our observed luminosities and timescales. For a standard on-axis afterglow, the extrapolation of the observed flux would violate the upper limits reported by Evans et al. (LVC GCN 21550), and Cenko et al. (LVC GCN 21572). Our observations are instead consistent with the onset of an off-axis afterglow from the GRB jet. This would explain the low luminosity of the observed gamma-ray emission, and the lack of early afterglow detections. Further observations are planned. We thank Belinda Wilkes and the entire CXC staff for rapidly scheduling these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21768 SUBJECT: LIGO/Virgo G298048: GMRT Follow-up of SSS17a at 1.4 GHz DATE: 17/08/30 16:06:24 GMT FROM: Nial Tanvir at U of Leicester L. Resmi (IIST), K. Misra (ARIES), N. R. Tanvir (U. Leicester), P. T. OBrien (U. Leicester) and S. Schulze (Weizmann Institute of Science) report on behalf of a larger collaboration. We observed the LIGO/Virgo G298048 source SSS17a (Coulter et al. LVC GCN Circ. 21529) with the Giant Meterwave Radio Telescope (GMRT) on 25 Aug 2017 10.5 UT at 1390 MHz for a total integration time of 2 hours. Preliminary analysis of the data does not reveal any emission at the location of the optical transient up to a 3-sigma upper limit of 130 micro Jy. We report a weak detection of ~ 160 micro Jy at RA(2000) = 13:09:47.74 Dec(2000) = -23:23:01.24 with a positional uncertainty of 3". This is consistent with the position of the optical host galaxy and the JVLA/ALMA radio source reported by Alexander et al. (LVC GCN Circ 21589) and Williams et al (LVC GCN Circ 21750). Further analysis is underway. Continued follow-up observations are planned. We thank the GMRT staff for prompt scheduling of these observations. The GMRT is run by the National Center for Radio Astrophysics of the Tata Institute of Fundamental Research. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21778 SUBJECT: LIGO/Virgo G298048: Continued Gemini South observations DATE: 17/08/31 18:28:50 GMT FROM: Eleonora Troja at GSFC/Swift E. Troja (UMD/GSFC), N. Butler (ASU), A. Watson (UNAM), S. Covino (INAF), W. H. Lee (UNAM), J. Becerra-Gonzalez (UMD/GSFC), A. Lien (UMBC), T. Sakamoto (AGU), and P. D'Avanzo (INAF): We continued optical and near-infrared observations of SSS17a (Coulter et al., LVC GCN 21529). The source appears substantially fainter than in our previous observations ( Troja et al., LVC GCN 21682), consistent with the rapid NIR fading reported by Chornock & Berger (LVC GCN 21684). However, over the course of the last three nights, the NIR countepart appears to have flattened inthe Ks-band at a level of ~17.7 mag. We thank the entire Gemini-South staff and the director, Laura Ferrarese, for their support of these observations. [GCN OPS NOTE(31aug17): Per author's request, the middle sentence as added to the first paragraph.] //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21779 SUBJECT: LIGO/Virgo G298048: Possible Plateau in Ks band revealed by continued Gemini-South observations DATE: 17/08/31 18:32:01 GMT FROM: Leo Singer at NASA/GSFC L. P. Singer (NASA/GSFC), R. Lau (Caltech), and M. M. Kasliwal (Caltech) report on behalf of the Global Relay of Observatories Watching Transients Happen (GROWTH) collaboration: We report continued near-infrared observations in J, H, Ks band on the FLAMINGOS-2 instrument on Gemini-South through 2017-08-31 UT. The source seems to have ceased fading between 2017-08-28 UT and 2017-08-29 UT and reached a plateau at about Ks = 17.7 mag (Vega). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21780 SUBJECT: LIGO/Virgo G299232: XSNAOC spectral observation of MASTER OTJ033744.97+723159.0 DATE: 17/08/31 20:24:41 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs Liming Rui (Tsinghua University), Xiaofeng Wang (Tsinghua university), Danfeng Xiang (Tsinghua Univeristy), Han Lin (Tsinghua Unviersity), and Huijuan Wang (NAOC) We obtained an optical spectrum (range 380-870 nm) of MASTER OTJ033744.97+723159.0 (Lipunov et al. GCN 21720, GCN2136), on 2017-08-29.54UT with the 2.16-m telescope at Xinglong Station of National Astronomical Observatories of China (NAOC) on BFOSC (Beijing Faint Object Spectrograph and Camera). The spectrum is consistent with a type IIb supernova a few days before the maximum light, using SN96cb data as the spectral templates. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21781 SUBJECT: LIGO/Virgo G298048: Hubble Space Telescope observations DATE: 17/08/31 20:33:24 GMT FROM: Nial Tanvir at U of Leicester A.J. Levan (Warwick), E. Troja (UMD/GSFC), N.R. Tanvir (Leicester), O. Fox (STScI), J. Hjorth (DARK, Copenhagen), S. B. Cenko (GSFC), A. S. Fruchter (STScI), R. Ryan (STScI), Z. Cano (Granada), A. de Ugarte Postigo (Granada), P. Evans (Leicester), J. Greiner (MPE Garching), N. Kawai (Tokyo Tech), H. Khandrika (STScI), A. Lien (UMBC/GSFC), J. Lyman (Warwick), I. Mandel (Birmingham), P. O'Brien (Leicester), J. Osborne (Leicester), E. Palazzi (INAF-IASF Bologna), D. Perley (LJMU), E. Pian (INAF-IASF Bologna), L. Piro (INAF/IAPS), T. Sakamoto (AGU), S. Schulze (Weizmann Institute of Science), S. Rosswog (Stockholm), D. Steeghs (Warwick), P. Sutton (Cardiff), D. Watson (DARK, Copenhagen) report: We obtained both multi-wavelength imaging and spectroscopy of the proposed counterpart (LVC GCN 21529) of LIGO/Virgo G298048 (LVC GCN 21509) with the Hubble Space Telescope at several epochs between 22 and 28 August (under programmes GO 14804 (Levan), GO 14850 (Troja) and GO 14771 (Tanvir)). The transient is well detected in both the nIR and optical imaging, but is fading rapidly at the end of the observations, with a factor two fading between Aug 26 and Aug 28 in the F160W filter. Spectroscopy at the first epoch covers the range 0.9-1.6 microns, and the counterpart is well detected across this spectral range. The spectrum is dominated by a range of broad features, most notably a peak at ~1.1 microns, but additional features are observed between 1.2 and 1.6 microns. An image of the field, as observed by HST is shown at http://www.astro.warwick.ac.uk/people/levan/gw_hst001 NOTE: The page is password protected with password HsT_G298048, and the image should not be shared. We thank the staff of STScI, in particular Patrica Royle, Alison Vick, Neill Reid and Lou Strolger for their rapid work in scheduling these ToO observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21783 SUBJECT: LIGO/Virgo G298048 DATE: 17/09/01 21:54:25 GMT FROM: Adam Zadrozny at Pi of the Sky A. Cwiek (NCBJ), A. F. Zarnecki (UW), A. Mankiewicz (CFT PAS), A. Zadrozny (UTRGV, NCBJ) on behalf of the Pi of the Sky Pi of the Sky telescope surveyed area (RA: 220 - 22 deg, DEC: -10 - 70) that overlap, in parts, with initial bayesstar skymap for G298048. Observations were conducted from INTA, Huelva Spain during nights 17th up to 21th of August. Is it worth noting that this area was well observed from 10th up 16th August giving a strong reference background. Data was searched for any type of transients connected with objects from GLADE catalogue. Data analysis showed that it is unlikely to have an slowly fading optical transient. However two possible fast fading optical transients are still under investigations along with several other subprimes. Investigated possible optical transients with positions: RA DEC 20.876109 33.322977 354.050166 14.997596 We have performed our observations using two cameras using only IR-cut filter. Each camera have 20 by 20 degree field of view. For each observed field (20 by 20 degrees), the telescope has made five 10 s exposures twice a night. Observations have limiting brightness between 11.5 - 12 mag. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21785 SUBJECT: LIGO/Virgo G298048: AGILE-GRID analysis of data contemporary to X-ray emission from SSS17a in NGC4993 DATE: 17/09/02 16:54:59 GMT FROM: Francesco Verrecchia at ASDC, INAF-OAR F. Verrecchia (SSDC and INAF/OAR), M. Cardillo (INAF/IAPS), A. Bulgarelli (INAF/IASF-Bo), M. Tavani (INAF/IAPS, and Univ. Roma Tor Vergata), G. Piano (INAF/IAPS), M. Pilia (INAF/OA-Cagliari), I. Donnarumma (ASI), C. Pittori (SSDC and INAF/OAR), F. Longo (Univ. Trieste and INFN Trieste), A. Ursi, G. Minervini, A. Argan, Y. Evangelista (INAF/IAPS), F. Lucarelli (SSDC and INAF/OAR), N. Parmiggiani, A. Zoli, V. Fioretti, F. Fuschino (INAF/IASF-Bo), A. Trois (INAF/OA-Cagliari), M. Marisaldi (INAF/IASF-Bo and Bergen University), A. Giuliani (INAF/IASF-Mi), report on behalf of the AGILE Team: We performed a dedicated analysis of AGILE Gamma-Ray Imaging Detector (GRID) data in response to the detection on 2017-08-26 by Chandra of an X-ray transient (Troja et al., LVC GCN 21765). This source is coincident with the optical/IR transient SSS17a (Coulter et al., LVC GCN 21529) possibly associated with GW170817A. GRID data analysis covering the SSS17a position was performed in the energy range 50 MeV - 10 GeV with integration times from 1 to 3 days centered at T0+9 days. Preliminary values of 2-sigma upper limits (UL) are reported below: 3.0e-10 erg cm^-2 s^-1 for a 1-day integration time (from 26 August 00:00 UT to 27 August 00:00 UT); 1.9e-10 erg cm^-2 s^-1 for a 2-day integration time (from 26 August 00:00 UT to 28 August 00:00 UT); 1.3e-10 erg cm^-2 s^-1 for a 3-day integration time (from 25 August 00:00 UT to 28 August 00:00 UT). These measurements were obtained with AGILE observing a large portion of the sky in spinning mode. Additional analysis of AGILE data is in progress. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21786 SUBJECT: LIGO/Virgo G298048: Continued X-ray monitoring and X-ray detection of GW170817 [erratum]] DATE: 17/09/02 16:57:54 GMT FROM: Raffaella Margutti at Northwestern U W. Fong, R. Margutti (Northwestern), D. Haggard (McGill) report on behalf of a larger collaboration: We analyzed observations of the field of the EM counterpart to LVC trigger G298048 with the Chandra X-ray Observatory (CXO; ObsID 20728, PI Troja) starting on 2017 Sep 1.640 UT (15.1 days after the LVC trigger time). In 50 ksec of observations, we clearly detect X-ray emission at the location of the optical transient (Coulter et al., LVC GCN 21529; Allam et al., LVC GCN 21530; Sheng Yang et al., LVC GCN 21531; Chambers et al., LVC GCN 21553), suggesting continued X-ray emission from the transient (Troja et al., LVC GCN 21765). Extended emission from the host galaxy (Margutti et al., LVC GCN 21648; Evans et al., LVC GCN 21612) is still detected. We also note the presence of a third X-ray source in the Swift/XRT error circle (Evans et al., LVC GCN 21612; RA,Dec = 13:09:48.014,-23:23:04.93), that has not been previously reported. We thank Belinda Wilkes and the entire Chandra team for their great support with these observations. [GCN OPS NOTE(03sep17): This circular (21786) completely replaces 21784 (whose text was the result of a copy-paste mistake).] //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21787 SUBJECT: LIGO/Virgo G298048: Chandra monitoring of the X-ray emission from SSS17a DATE: 17/09/02 17:06:21 GMT FROM: Eleonora Troja at GSFC/Swift E. Troja (UMD/GSFC), L. Piro (INAF/IAPS), T. Sakamoto (AGU), S. B. Cenko (NASA/GSFC), and A. Lien (UMBC/GSFC) report on behalf of a larger collaboration: We re-observed the field of SSS17a (Coulter et al., LVC GCN 21529) with the Chandra X-ray Observatory (PI: E. Troja) on 2017-09-01 (~15 days after the LVC trigger) for a total exposure of 47 ks. The X-ray source reported in Troja et al. (LVC GCN 21765) is still detected. At the position of the optical/IR transient we measure ~17 net counts. By describing the spectrum with an absorbed power-law we estimate a flux of approximately 4.5E-15 erg/cm2/s (0.5-8.0 keV). We thank Belinda Wilkes and the entire Chandra team for approving and scheduling these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21798 SUBJECT: LIGO/Virgo G298048: Chandra X-ray Update on GW170817 DATE: 17/09/03 20:24:16 GMT FROM: Daryl Haggard at McGill U D. Haggard, M. Nynka (McGill), V. Kalogera (Northwestern), Phil Evans (Leicester), and Brad Cenko (NASA/GSFC) We report a new ~47 ks Chandra X-ray observation (ObsID 18988, PI Haggard) of the LVC trigger G298048, a.k.a. GW170817, beginning 2017 September 02, approximately 16 days after the trigger. These observations include the optical transient SSS17a (Coulter et al., LVC GCN 21529) and the Swift area of interest (Evans et al., LVC GCN 21612). We detect X-ray emission from two point sources and from one extended source: (i) point-source X-ray emission at the location of the optical transient SSS17a (Coulter et al., LVC GCN 21529; Troja et al., LVC GCN 21765; Margutti LVC GCN 21786; Troja et al., LVC GCN 21787), (ii) another point source at the location of the Swift X-ray emission (Evans et al., LVC GCN 21612) also reported by Margutti et al. (LVC GCN 21786), and (iii) extended emission from the host galaxy NGC 4993 (Evans et al., LVC GCN 21612; Margutti et al., LVC GCN 21648). We analyze these new data in combination with DDT Chandra observations acquired one day earlier (ObsID 20728, PI Troja) and report tentative evidence for decreasing fluxes from both X-ray point sources (1-sigma errors are ~1E-15 erg/s/cm2): X-ray Counterpart to Optical Transient SSS17a (assuming PL w/ gamma=2.4): Sep 01: 5.1E-15 erg/s/cm2 (0.3-8 keV) Sep 02: 4.5E-15 erg/s/cm2 (0.3-8 keV) Chandra X-ray Point Source (assuming PL w/ gamma=2.0): Sep 01: 3.5E-15 erg/s/cm2 (0.3-8 keV) Sep 02: 2.7E-15 erg/s/cm2 (0.3-8 keV) We thank Belinda Wilkes and the entire Chandra team for their support of these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21803 SUBJECT: LIGO/Virgo G298048: ATCA monitoring of SSS17a in NGC 4993 DATE: 17/09/04 02:26:14 GMT FROM: Eleonora Troja at GSFC/Swift E. Troja (UMD/GSFC), R. Ricci (INAF), M. Wieringa (CSIRO), and L. Piro (INAF) report: On 01 Sep 2017, we observed the field of SSS17a (Coulter et al., LVC GCN 21529) with the Australia Telescope Compact Array (ATCA) at the central frequencies of 16.7, 21.2, 43 and 45 GHz, each with a bandwidth of 2 GHz. At the position of the optical/IR and X-ray source (Troja et al., LVC GCN 21765, 21787) we report the following 3-sigma upper limits: 17/21 GHz      < 50 uJy 43/45 GHz      < 90 uJy Further observations are planned. We thank the CSIRO staff for approving and executing these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21804 SUBJECT: LIGO/Virgo G298048: e-MERLIN upper limits on 5 GHz compact emission from SSS17a DATE: 17/09/04 07:48:43 GMT FROM: Zsolt Paragi at Euro VLBI Javier Moldon and Rob Beswick (JBO-Manchester University) for the EuroVLBI team We monitored the field around the optical counterpart SSS17a (Coulter et al., LVC 21529) with the e-MERLIN radio interferometer between August 23 and 28, 2017. We conducted observations at C band centred at 5 GHz with a bandwidth of 512 MHz for 5 hours between 13:00 and 18:00 UTC in each consecutive day. No significant detection above 5-sigma level is found in the runs with individual rms noise levels between 31 and 39 microJy/beam. The upper limits at 5-sigma level are 180, 160, 160, 190, 150, 150 microJy/beam for days 23 to 28 August, respectively. The average half power beam width of the images is 266 mas x 33 mas with a position angle of 0 degrees. An image produced combining the data from the six runs yields an upper limit of 70 microJy/beam at the 5-sigma level. Additional observations are planned with e-MERLIN to continue the monitoring of the transient source. e-MERLIN is a National Facility operated by the University of Manchester at Jodrell Bank Observatory on behalf of STFC. -- Zsolt Paragi Head of User Support Joint Institute for VLBI ERIC (JIVE) Web: http://www.jive.eu Oude Hoogeveensedijk 4 Phone: +31 (0)521-596-536 7991 PD Dwingeloo Mobile: +31 (0)629-034-718 the Netherlands Fax: +31 (0)521-596-539 //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21814 SUBJECT: LIGO/VIRGO G298048: Radio detection of SSS17a at 3GHz with the VLA/JAGWAR DATE: 17/09/04 22:14:55 GMT FROM: Kunal Mooley at U of Oxford [8] K. P. Mooley (Hintze Fellow, Oxford), G. Hallinan (Caltech) and A. Corsi (TTU) report on behalf of the JAGWAR and GROWTH teams We observed the location of SSS17a in S band (2-4 GHz) as part of the Jansky Array mapping of GW bursts as Afterglows in Radio (JAGWAR) program on 01-02 Sep 2017 for 5 hours. We report the detection of a source with a signal-to-noise ratio of ~5, consistent within the astrometric uncertainty of the optical transient (Coulter et al. 2017, LVC GCN 21529). We have confirmed this source through comparison with contemporaneous C band observations reported by Corsi et al. (see companion LVC GCN). Multifrequency monitoring of this source with the VLA and other radio facilities has been initiated. We thank the VLA staff for scheduling these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21815 SUBJECT: LIGO/VIRGO G298048: Radio detection of SSS17a at 6 GHz with the VLA DATE: 17/09/04 22:14:59 GMT FROM: Alessandra Corsi at Texas Tech U. A. Corsi (TTU), G. Hallinan (Caltech), K. Mooley (Hintze Fellow, Oxford), D.A. Frail (NRAO), M.M. Kasliwal (Caltech), N.T. Palliyaguru (TTU) report on behalf of a larger GROWTH collaboration: We observed the field of SSS17a/DLT17ck (e.g., Coulter et al. LVC GCN 21529; Allam et al. LVC GCN 21530; Yang et al. LVC GCN 21531), the possible counterpart of G298048 (LVC, LVC GCN 21505) in NGC 4993, with the Karl G. Jansky VLA in its B configuration (program 16A-206; PI: Corsi). The observation lasted about 1.25 hr, starting on 17-Sep-03 23:30:57 UT, and was conducted in C-band (approximate central frequency of 6 GHz). We report the detection of a radio source with S/N of about 5. This source was not seen in previous epochs down to similar limits (e.g. Corsi et al., LVC GCN 21664). The radio position is within the astrometric errors of the optical position of SSS17a. We have confirmed this source through comparison with contemporaneous S-band observations reported by Mooley et al. (see companion LVC GCN by Mooley et al.). Further observations are planned immediately. We thank the VLA staff for scheduling these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21816 SUBJECT: LIGO/VIRGO G298048: Precise position of SSS17a based on HST and Gaia DATE: 17/09/05 00:30:09 GMT FROM: Mansi M. Kasliwal at Caltech S. M. Adams, M. M. Kasliwal, N. Blagorodnova (Caltech) report on behalf of a larger GROWTH (Global Relay of Observatories Watching Transients Happen) collaboration We registered our HST F336W image (PI Kasliwal) with the Gaia astrometric catalog to derive a more precise position of SSS17a (Coulter et al. LVC GCN 21529). We find a position of 13:09:48.071 -23:22:53.37 with astrometric residuals of 0.05". This new position is consistent with the position of the radio source reported in companion GCNs by Corsi et al. LVC GCN 21815 and Mooley et al. LVC GCN 21814. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21833 SUBJECT: LIGO/Virgo G298048 GRAWITA: VST-ESO PARANAL follow up of SSS17a in NGC4993. DATE: 17/09/06 15:07:27 GMT FROM: Aniello Grado at INAF-OAC A. Grado (INAF-OAC), F. Getman (INAF-OAC), L. Limatola (INAF-OAC), E. Cappellaro (INAF-OAPD), M. Branchesi (GSSI), S. Covino (INAF-OAB), P. D'Avanzo (INAF-OAB), A. Melandri (INAF-OAB), L. Amati (INAF-IASF Bo), L. A. Antonelli, (INAF-OAR), S. Ascenzi (INAF-OAR), S. Benetti (INAF-OAPD), M.T. Botticella (INAF-OAC), S. Campana (INAF-OAB), V. D'Elia (INAF-ASDC), D. Fugazza, M. Lisi (INAF-OAR), G. Greco (Urbino University/INFN Firenze), L. Nicastro (INAF-IASF Bo), E. Palazzi (INAF, IAFS Bo), E. Pian (INAF, IAFS Bo), S. Piranomonte (INAF-OAR), L. Pulone (INAF-OAR), A. Rossi (INAF-IASF Bo), P. Schipani (INAF-OAC), G. Stratta (Urbino University/INFN Firenze), G. Tagliaferri (INAF-OAB), V. Testa (INAF-OAR), L . Tomasella (INAF-OAPD), S. Yang (INAF-OAPD), E. Brocato (INAF-OAR) on behalf of GRavitational Wave Inaf TeAm report: Observations of 1 square degrees of the skymap of the Advanced LIGO and Virgo trigger G298048 (LVC GCN Circ. 21509, 21513) were performed with the VLT Survey Telescope (VST - Proposal ID ESO 099.D-0191) at ESO-Paranal equipped with OMEGACAM. The observations are centered on the galaxy NGC4993. The images were taken in the i_SDSS filter with a total exposure of 1200s. The observations started at 2017-08-31T 23:22:12.442 UTC and finished at 2017-08-31T 23:39:26.585. The Optical Transient (OT) is not visibile in the coadded image. The completeness at 50% for point-like sources is 22.53 AB mag. Automatic data reduction with the VSTTube pipeline (Grado et al. 2012 Mem.SAIt 19, 362 ) was completed. We acknowledge excellent support from the ESO User Support Department and from ESO observing staff in Paranal. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21842 SUBJECT: LIGO/Virgo G298048: ATCA observations of of SSS17a in NGC 4993 DATE: 17/09/07 02:31:55 GMT FROM: Tara Murphy at U of Sydney T. Murphy (University of Sydney), E. Lenc (University of Sydney), C. Lynch (University of Sydney), D. Dobie (University of Sydney), D. Kaplan (UWM), K. Bannister (CSIRO), on behalf of the VAST collaboration. Following the reported VLA detection of a radio source (Mooley et al.; LVC GCN 21814, Corsi et al.; LVC GCN 21815) coincident with the optical transient SSS17a (Coulter et al. LVC GCN 21529) we conducted further observations of NGC 4993 with the Australia Telescope Compact Array at 5.5 and 9 GHz. Observations started at 2017-09-04 22:43:04 UT and ended at 2017-09-05 10:03:04 UT with approximately 9.5 hours of on-source time. We did not make a robust detection, although there is marginal emission at the 4-sigma level, at a position consistent with that reported by Mooley at al. and Corsi et al. This could be associated with the host galaxy or the optical transient. Analysis is ongoing, and subsequent epochs are planned. Thank you to CSIRO staff for supporting these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21848 SUBJECT: LIGO/Virgo G298048: LWA Detection DATE: 17/09/08 02:47:01 GMT FROM: Christopher League at FRBSG T. Callister (Caltech), J. Dowell (U New Mexico), J. Kanner (Caltech), M. Kavic (LIU Brooklyn), C. League (LIU Brooklyn), P. Shawhan (U Maryland), J. Simonetti (Virginia Tech), G. Taylor (U New Mexico), J. Tsai (Virginia Tech), C. Yancey (U Maryland) We report the preliminary detection of a radio source in a beam centered on RA 13.096h, Dec -22.024deg, the LIGO/Virgo G298048 event coordinates, during a four-hour observation on August 17 (19:15 UTC, 6.6 hours after the GW trigger), using station 1 of the Long Wavelength Array (LWA1) [GCN 21680]. Simultaneous ON-OFF observations were taken at 25 MHz and 45 MHz, and follow-up observations were taken August 24 (19:50 UTC), one week after the initial observations. Comparison of the ON-OFF observations for the two epochs indicate the apparent presence of a ~20 Jy source, at 25 MHz, in the beam on RA 13.096h, Dec -22.024deg. There is no difference between the ON-OFF results at 45 MHz, for the two epochs. Further analysis and follow up observations are underway. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21850 SUBJECT: LIGO/Virgo G298048: VLBA upper limits at 8.7GHz for the GW counterpart SSS17a/DLT17ck on August 20-21 UT DATE: 17/09/08 11:16:27 GMT FROM: Igor Andreoni at Swinburne U of Tech A. Deller (Swinburne/OzGrav), M. Bailes (Swinburne/OzGrav), I. Andreoni (Swinburne/OzGrav/AAO), K. Bannister (CSIRO), J. Cooke (Swinburne/OzGrav), D. Dobie (University of Sydney), D. Kaplan (UWM), C. Lynch (University of Sydney), T. Murphy (University of Sydney), on behalf of a joint effort between OzGrav and the VAST collaboration. Radio observations with the Very Long Baseline Array from 2.5 weeks ago (Deller et al., LVC GCN 21588) covering the field surrounding the optical transient SSS17a/DLT17ck (e.g., Coulter et al., LVC GCN 21529; Allam et al., LVC GCN 21530; Yang et al., LVC GCN 21531) have now been correlated and analysed. Each observation spanned 6.5 hours, with 256 MHz of bandwidth (dual polarisation) centered on 8.7 GHz, giving an image rms of approximately 22 microJy. A 12500x12500 pixel image (2.5 x 2.5") image was produced, centered on SSS17a/DLT17ck. As expected given non-detections with the VLA (Alexander at al., LVC GCN 21589; Corsi et al., LVC GCN 21613; Corsi et al., LVC GCN 21614; Corsi et al., LVC GCN 21636) and ATCA (Bannister at al., LVC GCN 21559; Kaplan et al., LVC GCN 21574; Lynch et al., LVC GCN 21670) close in time to these VLBA observations, we do not detect any radio emission, and place 5.5 sigma upper limits as follows: Observation center MJD 57985.9: 5.5 sigma upper limit 125 microJy. Observation center MJD 57986.9: 5.5 sigma upper limit 120 microJy. Combining these two observations places a deeper limit, with image rms 16 microJy: 5.5 sigma upper limit 88 microJy. We thank the staff of the Long Baseline Observatory for supporting these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21851 SUBJECT: LIGO/Virgo G298048: VLA radio non-detection DATE: 17/09/08 13:23:16 GMT FROM: Kate Alexander at Harvard U K. D. Alexander, E. Berger, T. Eftekhari, W. Fong, and R. Margutti report on behalf of a larger collaboration: We observed the location of the optical counterpart of LIGO/Virgo G298048 (Coulter et al. LVC GCN 21529; Allam et al. LVC GCN 21530) with the Very Large Array at a frequency of 6 GHz (C-band) on September 5.925 UT. We do not detect any significant radio emission (S/N>3) and therefore cannot confirm the radio detection reported two days earlier by Corsi et al. (LVC GCN 21815) for a comparable integration time on source and at the same frequency. This indicates either rapid fading (not expected for off-axis jet emission), significant variability (not expected from scintillation given the small source distance and hence large angular size), or a spurious detection in the previously reported observations. Further observations are underway. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21882 SUBJECT: LIGO/Virgo G298048: ATCA monitoring of SSS17a in NGC 4993 DATE: 17/09/14 05:25:42 GMT FROM: Eleonora Troja at GSFC/Swift M. Wieringa (CSIRO), R. Ricci (INAF), L. Piro (INAF) and E. Troja (UMD/GSFC) report: On 08 Sep 2017, we observed the field of SSS17a (Coulter et al., LVC GCN 21529) with the Australia Telescope Compact Array (ATCA) at the central frequencies of 16.7 and 21.2 GHz, each with a bandwidth of 2 GHz. At the position of GW counterpart (Adams et al., LVC GCN 21816) we report the following 3-sigma upper limit: 17/21 GHz < 35 uJy Further observations are planned. We thank the CSIRO staff for approving and executing these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21883 SUBJECT: LIGO/Virgo G298048: AST3-2 observations of SSS17a/DLT17ck from Antarctica DATE: 17/09/15 03:45:21 GMT FROM: Igor Andreoni at Swinburne U of Tech Lei Hu (Purple Mountain Observatory), Lifan Wang (Texas A&M University/Purple Mountain Observatory), Tianrui Sun (Purple Mountain Observatory), Ma Bin (National Astronomical Observatory of China), Xiaofeng Wang (Tsinghua University), Xuefeng Wu (Purple Mountain Observatory), and the AST3 team and Jeff Cooke (Swinburne/OzGrav), Igor Andreoni (Swinburne/OzGrav/AAO) on behalf of OzGrav We report observations of the GW counterpart SSS17a/DLT17ck (e.g., Coulter et al., LVC GCN 21529; Allam et al., LVC GCN 21530; Yang et al., LVC GCN 21531) with the second of Antarctica Schmidt Telescopes (AST3-2). AST3-2 is a 50cm optical telescope located at Kunlun Station at Dome A in the Antarctic. Observations were carried out from August 18 through August 28 in g-band filter. Data transfer from Antarctica has recently completed. A source with g-band magnitude 18.15 +/-0.1 was detected on 2017-08-18T14:42.6796 (mean value) at the position of SSS17a/DLT17ck. Note the signal was identified from a coadded image and the observational information about the component images are as follows. Image-ID UT datetime of start of observation Exposure time 0818-48 '2017-08-18T13:58:11.6138' 300.00 0818-49 '2017-08-18T14:03:14.8497' 300.00 0818-50 '2017-08-18T14:09:07.4807' 300.00 0818-51 '2017-08-18T14:14:10.7166' 300.00 0818-52 '2017-08-18T14:28:36.9730' 300.00 All observation from AST3-2 are reported below. All time mentioned is UT time of start of exposure: August 18 The observation is not regular, so we list them in details Group1: observation started from [ID 48]2017-08-18T13:58:11.6138 to [ID 51]2017-08-18T14:14:10.7166 Total 4 images with constant exposure time 300s and regular cadence about 54s Group2: observation started from [ID 52]2017-08-18T14:28:36.9730 to [ID 72]2017-08-18T17:57:39.5806 Total 21 images with constant exposure time 300s and regular cadence about 54s August 20 observation started from [ID 15]2017-08-20T12:51:40.934 to [ID 74]2017-08-20T18:43:29.7538 Total 60 images with constant exposure time 300s and regular cadence about 54s August 21 observation started from [ID 6]2017-08-21T13:10:22.4063 to [ID 55]2017-08-21T17:58:16.8969 Total 50 images with constant exposure time 300s and regular cadence about 54s August 23 observation started from [ID 692]2017-08-23T13:13:02.8477 to [ID 722]2017-08-23T16:10:14.0793 Total 31 images with constant exposure time 300s and regular cadence about 54s August 24 observation started from [ID 871]2017-08-24T15:52:00.3374 to [ID 917]2017-08-24T20:36:43.9922 Total 47 images with constant exposure time 300s and regular cadence about 54s August 25 observation started from [ID 1153]2017-08-25T14:07:25.7058 to [ID 1168]2017-08-25T15:36:08.5704 Total 16 images with constant exposure time 300s and regular cadence about 54s August 27 observation started from [ID 1204]2017-08-27T13:50:45.9777 to [ID 1223]2017-08-27T15:43:31.4251 Total 20 images with constant exposure time 300s and regular cadence about 54s August 28 observation started from [ID 731]2017-08-28T15:12:09.9744 to [ID 738]2017-08-28T15:52:53.1212 Total 8 images with constant exposure time 300s and regular cadence about 54s Processing of the AST3-2 images is in progress. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21886 SUBJECT: LIGO/Virgo G298048: ATLAS pre-discovery limits 601 to 16 days before first detection of SSS17a/DLT17ck DATE: 17/09/15 11:24:15 GMT FROM: S. J. Smartt at Queens U Belfast J. Tonry (IfA), K. W. Smith (QUB), L. Denneau, A. Heinze, B. Stalder, H. Weiland (IfA), C. W. Stubbs (Harvard), S. J. Smartt (QUB), A. Rest (STScI), K. C. Chambers (IfA), T.-W. Chen (MPE), M. Coughlin (Harvard), D. R. Young, (QUB), M. E. Huber (IfA), D. E. Wright (QUB), H. Flewelling, T. Lowe, E. A. Magnier, A. S. B. Schultz, C. Waters, R. J. Wainscoat, M. Willman (IfA) During its normal survey mode, the ATLAS survey project (Tonry et al. 2011, Stalder et al. 2017) frequently observed the field containing galaxy NGC4993 during the period between 57380.64463 and 57966.26370 (602 to 16 days before G298048; the LIGO Scientific Collaboration and the Virgo Collaboration GCN 21509) and the first discoveries and detections of the optical/NIR transient SSSa17a/DLT17ck (Coulter et al. GCN 21529, Allam et al. GCN 21530,Valenti et al. GCN21531, Melandri et al. 21532). We have completed a search for variability or eruptions at the position of the optical transient in the 414 images over this period. These images were taken typically with 4-5 images per night (30 second exposures). ATLAS observes in two wide-band filters, called "cyan" or "c:, which roughly covers the SDSS/Pan-STARRS g and r filters, and “orange” or "o", which roughly covers the SDSS/Pan-STARRS r and i. The position was observed 414 times in one or other filter and on each of these we forced flux measurements at the astrometric position of the transient on the difference image. We used the Pan-STARRS images for the astrometric postion of SSS17a/DLT17ck (Chambers et al. GCN 21553) We measured 5-sigma flux limits and any epochs with greater than 5-sigma detections. The 5-sigma flux limits were in the range 18.5 +/- 0.4 (AB mag, median and standard deviation) and (19.4 +/- 0.4). We found 44 images which formally had flux detections greater than 5-sigma, but on visual inspection we rule out these being real flux variability at the transient position. They all appear to be residuals from the host galaxy subtraction. With ATLAS, we rule out any variability down to 18.5 to 19.4 (filter dependent) during a period 601 to 16 days before discovery of the optical transient. The last image was on 57966.26370 (2017-08-01 06:19) with a 5-sigma limit of o < 18.2. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21889 SUBJECT: LIGO/Virgo G298048: Danish Telescope Observations of SSS17a/DLT17ck DATE: 17/09/15 16:40:07 GMT FROM: Zach Cano at U of Iceland ​Z. Cano (IAA-CSIC), U. G. Jorgensen (Univ. of Copenhagen), G. Hodosan (IAA-CSIC, Univ. of St Andrews), R. Figuera Jaimes (Univ. of St Andrews), Y. I. Fujii (Univ. of Copenhagen; Nagoya Univ.), and M. Rabus (Pontificia Univ. Catolica de Chile, MPIA) We report on observations obtained with the 1.54-m Danish Telescope located at La Silla, Chile, of the GW counterpart SSS17a/DLT17ck (Coulter et al., LVC GCN 21529). Observations were obtained on 2017, August 19th, 21st and 22nd in the I-band (all three dates), and z-band (19th only). A summary of the observations follows: Date UT Start Exposure time (s) Filter ---------------------------------------------------------------------- 19-August 23:41:45.6 6 x 150 I 19-August 23:44:49.9 6 x 150 z 21-August 23:17:51.8 25 x 100 I 22-August 23:23:57.3 40 x 100 I Image subtraction of the co-added I-band images obtained during the first two nights reveals a residual transient at the following position: RA, Dec (J2000): 13:09:48.11 -23:22:53.0 With an estimated uncertainty of ~0.5''. This position is consistent with that found by other groups within its uncertainty radius. Further analysis of the images is currently underway, including the precise photometric calibration of the optical transient.​ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21891 SUBJECT: LIGO/VIRGO G298048: MeerKAT observations of SSS17a DATE: 17/09/15 20:16:29 GMT FROM: Kunal Mooley at U of Oxford S. Goedhart (SKA South Africa) reports on behalf of a larger team: MeerKAT, currently being commissioned, observed the location of SSS17a (Coulter et al. 2017, LVC GCN 21529) in L band between 2017-08-25 and 2017-09-06. Preliminary analysis of the observation from 2017-09-06 does not reveal a radio afterglow, with a 3-sigma upper limit of 75 uJy at 1.5 GHz. Further observations and analysis are planned. We thank the SKA South Africa team for enabling these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21894 SUBJECT: LIGO/Virgo G298048: Desert Fireball Network simultaneous optical observations of the SSS17a/DLT17ck. DATE: 17/09/18 13:45:29 GMT FROM: David Kaplan at UW-Milwaukee P. J. Hancock, S. J. Tingay, J. S. de Gois, T. Booler (ICRAR, Curtin University), H. A. R. Devillepoix, P. A. Bland, M. C. Towner, E. K. Sansom, R. M. Howie (DFN, Curtin University), D. L. Kaplan (UWM) The Desert Fireball Network (DFN) is a network of 50 remote cameras located in the Western and South Australian desert designed for the detection and triangulation of Fireballs and bright meteors. The DFN cameras consist of a Nikon D800E camera equipped with a Samyang 8mm f/3.5 UMC Fish-eye CS II lens. The cameras capture full sky images with a cadence of 30s from sunset to sunrise every night of the year. We retrieved images from a camera located at Wooleen Station (27.0872 deg S, 116.1611 deg E). We analysed the images from the 17th of August from 12:39:28-12:49:28 UT: 2 minutes before the GW trigger to 7 minutes after. At this time the host galaxy NGC 4993 was at 20 degrees elevation, reducing the image sensitivity from 6th to 4th magnitude. The images show no persistent or transient sources in a 3 degree radius of NGC 4993, to a limiting visual magnitude of +4. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21895 SUBJECT: LIGO/Virgo G298048: TOROS photometry of SSS17a DATE: 17/09/18 16:22:27 GMT FROM: Mario Diaz at U of Texas M. Diaz, L. Macri, J.L. Nilo Castellon, B. Sanchez, C. Mendes, C. Colazo, M. Schneitter, C. Girardini, D. Garcia Lambas, M. Beroiz, A. Zadrozny, R. Camuccio, M. Castillo. J. Garcia for the TOROS collaboration We have completed the PSF photometry of the observations of GW170817 carried out at the T80S telescope and the EABA telescope on 08/18/2017 and 08/19/2017 (GCN 21619, GCN, 21620). We calibrated our measurements using the Pan-STARRS1 catalog available at STScI, using their reported PSF magnitudes and uncertainties. The mid-point of our observations was 1.467d after the GW trigger - LIGO/Virgo G298048- (Julian Date of 2457984.495). At that time, we measured magnitudes of g=18.60, r=17.99, i=17.80 with uncertainties of +-0.02 mag. Additionally with our observations utilizing the EABA telescope we obtained r=18.78+-0.03 at 2.456d after the GW trigger -LIGO/Virgo G298048-. _______________________________________ Mario C. Díaz Director Center for Gravitational Wave Astronomy and Professor Department of Physics and Astronomy The University of Texas Rio Grande Valley (956) 882-6690 FAX: (956) 882-6726 mario.diaz@utrgv.edu http://www.mariodiaz.org/ ______________________________________ No ceder Carhue al huinca. Calfucura (1873) //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21897 SUBJECT: LIGO/Virgo G298048: Milliarcsecond imaging of the NGC 4993 central radio source DATE: 17/09/19 07:51:22 GMT FROM: Igor Andreoni at Swinburne U of Tech A. Deller (Swinburne/OzGrav), M. Bailes (Swinburne/OzGrav), I. Andreoni (Swinburne/OzGrav/AAO), K. Bannister (CSIRO), J. Cooke (Swinburne/OzGrav), D. Dobie (University of Sydney), D. Kaplan (UWM), C. Lynch (University of Sydney), T. Murphy (University of Sydney), on behalf of a joint effort between OzGrav and the VAST collaboration. We have further analysed the Very Long Baseline Array (VLBA) observations of the field containing NGC 4993 and SSS17a/DLT17ck (Deller et al., LVC GCN 21588; Deller et al., LVC GCN 21850), producing images centered on the sub-mJy radio source at the centre of NGC 4993 (Alexander et al., LVC GCN 21545; Alexander et al., LVC GCN 21548; Bannister et al., LVC GCN 21559; Alexander et al., LVC GCN 21589; Corsi et al., LVC GCN 21614). The source is detected with a flux density of 0.22 mJy (9 sigma significance, flux calibration scale uncertainty estimated at 20%). The data is consistent with either an unresolved or marginally resolved source, while comparison with the flux densities estimated by the ATCA and VLA observations indicate that most (or possibly all) of the source flux is contained within this milliarcsecond-scale component. Taking the synthesized beam size of 2.5 x 1.0 mas as an upper limit to the source size, the inferred lower limit for the brightness temperature is 1.6 x 10^6 K, consistent with an AGN interpretation. The position obtained is 13:09:47.69398 -23:23:02.3195 (J2000), with estimated uncertainties (dominated by systematics) of <=1 mas in each coordinate. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21898 SUBJECT: LIGO/Virgo G298048: SSS17a photometry of CHILESCOPE observatory DATE: 17/09/19 18:09:03 GMT FROM: Alexei Pozanenko at IKI,Moscow A. Pozanenko (IKI), A. Volnova (IKI), E. Mazaeva (IKI), P. Minaev (IKI), A. Moskvitin (SAO RAS), M. Krugov (AFIF) report on behalf of IKI-GW follow-up collaboration: We report a photometry of the counterpart SSS17a/DLT17ck (Coulter et al. GCN 21529; Yang et al., GCN 21531) of LIGO/Virgo trigger G298048 (LIGO Scientific Collaboration and Virgo Collaboration, GCNs 21509, 21513) with RC-1000 1m telescope of CHILESCOPE observatory (GCNs 21618, 21635, 21644). The observations carried out in a clear filter in four epochs. We used last epoch (7.49278 days after trigger) to construct a mask for subsequent mask subtraction. The PSF photometry is based on several nearby USNO-B1.0 stars (R2 magnitudes). Photometry of the transient SSS17a/DLT17ck is following Date UT start t-T0 Filter Exp. OT Err. (mid, days) (s) 2017-08-19 23:30:33 2.46157 CR 10*180 19.12 0.06 2017-08-20 23:21:09 3.47840 CR 13*180 20.04 0.08 2017-08-21 23:32:09 4.49409 CR 22*180 20.14 0.12 2017-08-24 23:53:39 7.49278 CR 20*180 >21.0 (3 sigma upper limit) //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21899 SUBJECT: LIGO/Virgo G298048: Limits from an FRB search of SSS17a with the Parkes 64m Radio Telescope DATE: 17/09/21 02:38:29 GMT FROM: Igor Andreoni at Swinburne U of Tech Matthew Bailes (Swinburne University of Technology-OzGrav) on behalf of SUPERB and OzGrav collaborations. We report on Fast Radio Burst (FRB) search observations of GW counterpart SSS17a/DLTck (eg. Coulter et al., LVC GCN 21529) with the Parkes 64m Radio Telescope in FRB search mode. Two 1-hour observations were searched for FRBs with Dispersion Measures (DMs) ranging from 0 to 2000 pc/cc 2.5 days after the GW event. The start UT of the 1hr integrations was 2017-08-20 01:44:32 and 2017-08-20 02:50:14. No FRBs were detected with a flux limit of 1.4 Jy (w/64 us)^{-1/2} where w is the width of the FRB in microseconds. An FRB in the host galaxy might be expected to have a DM of ~55 pc/cc plus the unknown contribution from any remnant. FRBs of luminosity similar to those observed from the repeating FRB 121102 would be detected at the distance of NGC 4993 with very high significance (SNR>>100). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21900 SUBJECT: LIGO/Virgo G298048: ATCA monitoring of SSS17a in NGC 4993 DATE: 17/09/21 06:42:36 GMT FROM: Eleonora Troja at GSFC/Swift R. Ricci (INAF), M. Wieringa (CSIRO), L. Piro (INAF) and E. Troja (UMD/GSFC) report: On 15 Sep 2017, 3rd epoch of our monitoring campaign, we observed the field of SSS17a (Coulter et al.,LVC GCN 21529) with the Australia Telescope Compact Array (ATCA) at the central frequencies of 16.7 and 21.2 GHz, each with a bandwidth of 2 GHz. At the position of the optical/IR source (Adams et al., LVC GCN 21816) we report the following 3-sigma upper limit: 17/21 GHz flux density < 42 uJy We thank the CSIRO staff for approving and executing the observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21908 SUBJECT: LIGO/Virgo G298048: LCO FLOYDS and Gemini Spectroscopy DATE: 17/09/22 03:24:44 GMT FROM: Curtis McCully at Las Cumbres Observatory C. McCully, D. A. Howell, G. Hosseinzadeh, D. Hiramatsu, I. Arcavi, S. Vasylyev (UCSB/Las Cumbres Obs), S. Valenti (UC Davis) and L. P. Singer (NASA/GSFC), C. Fremling (Caltech), and M. M. Kasliwal (Caltech) on behalf of the GROWTH (Global Relay of Observatories Watching Transients Happen) collaboration report: We observed the optical transient, SSS17a/DLT17ck (Coulter et al., LVC GCN 21529) on 2017-08-19 08:36:22, +1.83 days after the LIGO/Virgo trigger G298048 (LVC GCN Circ. 21509, 21513), for one hour with the robotic FLOYDS instrument mounted on the Las Cumbres Observatory Faulkes Telescope South at the Siding Spring Observatory in Australia. We detect the continuum of the transient at low signal-to-noise level. We also observed SSS17a/DLT17ck on 2017-08-20 01:01:54, +2.51 days after the LIGO/Virgo trigger, with the Gemini Multi-Object Spectrograph (GMOS) on the Gemini-South 8-m telescope. We observed in our red setting for 763 seconds and 128 seconds in our blue setting until the telescope reached its altitude limit. We again detect the continuum at low signal to noise level due to the high airmass at which the observations were made and the limited exposure times due to observing constraints. We thank the LCO staff, specifically Mark Bowman and Mark Willis, and the Gemini staff, specifically Karleyne Silva and Laura Ferrarese, for their assistance with these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21914 SUBJECT: LIGO/Virgo G298048: SRT observations of SSS17a in NGC 4993 DATE: 17/09/22 19:06:44 GMT FROM: Enzo Brocato at INAF-OA Roma Giambattista Aresu, Matteo Bachetti, Franco Buffa, Marta Burgay, Marco Buttu, Teresa Caria, Ettore Carretti, Paola Castangia, Giuseppe Carboni, Silvia Casu, Raimondo Concu, Alessandro Corongiu, Gianluigi Deiana, Elise Egron, Antonietta Fara, Francesco Gaudiomonte, Vincenzo Gusai, Adelaide Ladu, Sara Loru, Silvia Leurini, Lino Marongiu, Andrea Melis, Pino Melis, Carlo Migoni, Sabrina Milia, Alessandro Navarrini, Andrea Orlati, Pierluigi Ortu, Stefano Palmas, Alberto Pellizzoni, Delphine Perrodin, Maura Pilia, Tonino Pisanu, Sergio Poppi, Andrea Possenti, Andrea Saba, Giampaolo Serra, Mauro Serrau, Gabriele Surcis, Alessio Trois, Valentina Vacca, Gian Paolo Vargiu - all from INAF Osservatorio Astronomico di Cagliari Viviana Casasola - INAF Osservatorio Astrofisico di Arcetri Giancarlo Ghirlanda - INAF Osservatorio Astronomico di Brera Simona Righini, Matteo Stagni - INAF Istituto di Radioastronomia di Bologna on behalf of GRAvitational Wave Inaf TeAm (GRAWITA) report:. Following the VLA detection of a radio source (Mooley et al., LVC GCN 21814; Corsi et al., LVC GCN 21815) coincident with the optical transient SSS17a/DLT17ck (Coulter et al. LVC GCN 21529; Allam et al., LVC GCN 21530; Yang et al., LVC GCN 21531), the possible counterpart of G298048 (LVC, LVC GCN 21505) in NGC 4993, we carried out observations of the field with the Sardinia Radio Telescope at 7.2 GHz (central frequency, with a bandwidth of 680 MHz). Observations were conducted on the days 2017-09-07, 2017-09-08, 2017-09-09, and 2017-09-19, for a total of approximately 18 hours of on-the-fly mapping over the entire region and about 8 minutes of on-source time. The target was observed at low elevations (<27 degrees) and the weather conditions were suboptimal for a large fraction of the observing time. Data were taken to image a field of 0.3x0.3 deg^2 centred on the position of the source that was reported to be detected with the VLA on 2017-09-03. Calibration and analysis were conducted following two different approaches: - according to the procedures described in Egron et al. (2017,MNRAS, 470, 1329), we did not detect any source and find an upper limit for a steady source at the position of the target of 1.5 mJy (1 sigma) and a global rms of the image of 0.9 mJy/beam (1 sigma); - by using the map-making software described in Carretti et al. (2010, MNRAS, 405, 1670), we did not detect any source at that position, at an upper limit of 0.5 mJy rms (1 sigma) as computed for a steady source. According to the condition of each single observation, we find an upper limit ranging between at most 1 and 3 mJy for each observing session. At present a refinement of the analysis is ongoing and observations at subsequent epochs and at higher frequencies are planned. -- Enzo Brocato INAF - Osservatorio Astronomico di Roma Via di Frascati 33, I-00040 Monteporzio Catone, Italy Phone: +39 0694286438 Fax: +39 06 9447243 skype: enzo.brocato URL: SpoT Group Homepage: www.oa-teramo.inaf.it/SPoT //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21920 SUBJECT: LIGO/Virgo G298048: Effelsberg 100-m Radio Telescope observations of SSS17a DATE: 17/09/23 20:34:41 GMT FROM: Samaya Nissanke at Redboud U M. Kramer, A. Kraus, R. Eatough (MPI fuer Radioastronomie) The 100-m Effelsberg telescope of the MPIfR observed the location of SSS17a (Coulter et al. 2017, LVC GCN 21529) using the position provided by Adams et al. (LVC GCN 21816). Observations were conducted at 5, 15 and 32 GHz; none of them detected a counterpart. Observations at 32 GHz were performed at 10/9/2017 at UT 13:35 with the 100m telescope under moderate weather conditions using its secondary focus 9mm multi-beam receiver. In total, six maps were performed on the position of SSS17a. Data analysis was done with the MPIfR’s software packages „Toolbox“ and „Nod3“ (see Müller et al., 2017). First, some weather effects were removed by subtracting the maps of one of the „Off“-Horns from the „On“-Horn. After some additional baseline adjustment, the data was averaged and calibrated in Jy. Calibration parameters were determined by a similar observation of 3C286. The rms of the final map was 30 mJy (due to imperfect weather conditions and low elevation). Efforts are ongoing to improve those limits. Observations at C-band were also conducted at 10/9/2017 13:10 UT. No source was detected and limits do not improve on previous reports (e.g. Paragi et al., LVC CGN 21763; Alexander et al., LVC CGN 21851). At a central frequency of 14.6 GHz, we used a cryogenically cooled receiver (summed polarisations for 128 spectral channels, across a bandwidth of 500 MHz, and with a data sampling interval of ∼ 65 us) on 15/9/2017 (MJD 58011.537210648) for approximately 4025 seconds. Data have been dedispersed in the range 0 to 50 000 pc cm−3 and analysed for periodic signals and transient burst like events (e.g. FRBs) using single pulse search tools in the presto software package (http://www.cv.nrao.edu/ sransom/presto/). For a 10-sigma detection threshold, we achieve the following limits to periodic signals: 76 uJy and 52 uJy for duty cycles of 10% and 5%, respectively. Note that at this frequency, weather effects can decrease the sensitivity by at least a factor of two. More accurate flux calibration using a noise diode and reference source is on-going. At this observing frequency our transient search has revealed signals that cannot yet be easily distinguished from terrrestrial radio interference. Sensitivity limits for transients depend upon the unknown intrinsic pulse width and pulse broadening factors, however for a single pulse of width 1,3,5 and 10 ms, and DM of 1000 pc cm−3 (smearing at the central frequecny channel = 10.414 us), we find 6-sigma flux density limits of 0.32, 0.19, 0.15 and 0.10 Jy respectively. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21927 SUBJECT: LIGO/Virgo G298048: MWA Observations of Error Region DATE: 17/09/25 22:30:34 GMT FROM: David Kaplan at UW-Milwaukee D. Kaplan (UWM), I. Brown (UWM), M. Sokolowski (Curtin University), R. Wayth (Curtin University), T. Murphy (University of Sydney), D. Dobie (University of Sydney), C. Lynch (University of Sydney), and K. Bannister (CSIRO) on behalf of the MWA collaboration. We have observed a 20 x 20 deg field-of-view centered on the LIGO/Virgo G298048 localization region (LVC GCN #21513) with the Murchison Widefield Array. We observed 2017-08-18 07:07 UT to 2017-08-18 09:35 UT at a central frequency of 185 MHz and with a bandwidth of 30 MHz. No emission was detected at the position of NGC 4993. The RMS noise was 17 mJy/beam (note that the array is in the process of being reconfigured, so only 5/16 of the tiles are operational). Analysis of subsequent epochs with the reconfigured array is underway. We thank the MWA Operations team for supporting these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21928 SUBJECT: LIGO/Virgo G298048: Limits from further FRB searches of SSS17a DATE: 17/09/26 02:00:59 GMT FROM: Matthew Bailes at Swinburne U Matthew Bailes (Swinburne University of Technology-OzGrav) on behalf of the SUPERB and OzGrav collaborations. We report on further Fast Radio Burst (FRB) search observations of GW counterpart SSS17a/DLTck (eg. Coulter et al., LVC GCN 21529) with the Parkes 64m Radio Telescope in FRB search mode. Three additional hours of data were retrieved and reduced from 0.38-0.5d after the GW event using the same observing setup as that used in GCN circular 28199. The observations commenced at UTC 2017-08-18 06:49:31 (2h) and UTC 2017-08-18 08:50:36 (1h). No FRBs were detected with a flux limit of 1.4 Jy (w/64 us)^{-1/2} where w is the observed width of the FRB in microseconds. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21929 SUBJECT: LIGO/VIRGO G298048: Latest 3 GHz Detection of Radio Counterpart to SSS17a DATE: 17/09/26 05:14:16 GMT FROM: Gregg Hallinan at Caltech G. Hallinan (Caltech), A. Corsi (TTU), K. Mooley (Hintze Fellow, Oxford), D.A. Frail (NRAO), M.M. Kasliwal (Caltech), report on behalf of a larger collaboration: Our collaboration (GROWTH, JAGWAR, Caltech-NRAO, TTU-NRAO) has continued to monitor the evolution of the radio counterpart to GW170817/SSS17a discovered on September 2,3, 2017 with the Jansky VLA (Mooley et al. LVC GCN 21814 and Corsi et al. LVC GCN 21815), with ongoing observations at frequencies of 1.4 GHz, 3 GHz and 6 GHz. Responding to a request for further information to help plan observations at other radio facilities, we are including details on the most recent detection at 3 GHz, wherein the source was detected at a flux density of 34 +/- 3.6 uJy on Sept 17 (UT). The full light curves and interpretation have been submitted for publication (Hallinan, Corsi et al.). We thank the VLA staff for scheduling these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21931 SUBJECT: LIGO/Virgo G298048: Summary of Pi of the Sky observations DATE: 17/09/26 21:17:49 GMT FROM: Adam Zadrozny at Pi of the Sky T. Batsch, A.J. Castro-Tirado, H. Czyrkowski, A. wiek, M. wiok, R. Dbrowski, M. Jelnek, G. Kasprowicz, A.Majcher, K. Maek, L. Mankiewicz, K. Nawrocki, . Obara, R. Opiela, L. W. Piotrowski, M. Siudek, M. Sokoowski, R. Wawrzaszek, G. Wrochna, A. Zadrony, M. Zaremba, A.F. arnecki (Pi of the Sky Collaboration) Pi of the Sky robotic wide field of view telescopes search for the possible EM transients in the sky scans performed twice a night. Each of the two observation sites (South telescope in Chile and the North one in Spain) can cover up to about 20000 sq. deg. with range up to about 12.5m. Dedicated algorithms search for brightness changes of objects listed in GLADE to detect optical transients that might be connected with those galaxies. In the analysis related to G29048 we considered data collected by Pi of the Sky North telescope located in Spain, near Huelva, between August 17 and August 21, while the earlier data collected between August 10 and August 16 were used as a reference. The observations were performed in wide visible band, with IR-cut and UV-cut filters only, to achieve deepest detection limit. For each scan field 10 images with 10s exposure were taken and stacked for the analysis. On the night of 20170817 we surveyed area that overlaped partially with the initial bayesstar skymap for G298048. Unfortunatly, the dedicated scan procedure was interupted twice that night by the GCN alerts, resulting in the event coverage reduced to only about 29% probability, even after including other data collected that night. Coverage of about 51% was expected for uninterupted scan procedure, as obtained on the following nights. Data was searched for any type of transients connected with objects from GLADE catalogue. No significant transient candidate remained after all selection cuts. We acknowledge hospitality and support of the INTA El Arenosillo Test Centre in Mazagn near Huelva, Spain. Fields covered with the sky scan procedure on 20170817 ------------------------------------------------------ Pointing (RA[deg],Dec[deg]) gives the center of 20x20 deg^2 FOV. Field name Pointing S0120_10_10 ( 10.8, -0.2) S0000+50_35 ( 16.9, 57.1) S0200+50_10 ( 17.7, 39.5) S0120_10_35 ( 29.4, 18.1) S0200+50_35 ( 47.0, 57.1) S0000+90_35 ( 61.0, 77.4) S1600+50_35 (227.7, 40.7) S1600+10_10 (230.2, 0.1) S0000+90_10 (244.6, 76.8) S1600+10_35 (249.2, 18.0) S1600+50_10 (257.5, 58.5) S1840+10_10 (270.4, 0.0) S2000+50_10 (287.8, 39.5) S1840+10_35 (289.3, 18.0) S2120+10_10 (310.6, -0.1) S2000+50_35 (317.1, 56.9) S2299+50_10 (317.6, 39.5) S2120+10_35 (329.4, 18.1) S2240+10_10 (330.5, -0.1) S2299+50_35 (347.0, 57.3) S0000+50_10 (348.0, 39.4) S2240+10_35 (349.5, 18.2) Fields covered with other sky observations on 20170817 ------------------------------------------------------ GRB170817_35 ( 39.2, 79.9), GRB170817_10 (250.2, 73.4), GRB170818_35 (312.4, 10.7), S0000-10_35 ( 9.0, -1.9), R0000+30_10 ( 11.3, 39.0), S0200+50_10 ( 17.7, 39.4), S0326+70_10 ( 33.0, 58.8), S0326+70_10 ( 33.2, 58.8), S0200+50_35 ( 47.0, 57.1), S0326+70_35 ( 89.9, 75.9), S1440+10_10 (210.2, 0.3), S1440+10_35 (229.0, 18.2), S1630+30_10 (236.9, 20.1), S1630+30_35 (258.5, 38.0), S2000-10_10 (289.8,-19.8), S2000-10_35 (308.7, -1.7), S2120-10_10 (309.8,-19.7), S2200+50_10 (317.4, 39.4), S2120-10_35 (328.9, -1.8), S2240+10_10 (330.4, -0.2), R0000+30_35 (349.6, 21.0), S2200+50_35 (346.7, 57.2), S2240+10_35 (349.3, 18.2), S0000-10_10 (350.0,-19.8), This message can be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21933 SUBJECT: LIGO/VIRGO G298048: Further MeerKAT observations of SSS17a DATE: 17/09/27 13:19:14 GMT FROM: Kunal Mooley at U of Oxford S. Goedhart (SKA South Africa) reports on behalf of a larger team: MeerKAT, currently being commissioned, observed the location of SSS17a (Coulter et al. 2017, LVC GCN 21529) in L band between 25-Aug-2017 and 17-Sep-2017. No radio afterglow is detected, with upper limits provided below. We also provide the flux density of the host galaxy NGC4993 for each of three epochs. The observations have an effective (unflagged) bandwidth of 0.22 GHz spanning 1.30-1.66 GHz, with a center frequency of 1.48 GHz. Observations done on 25-27 August were reduced together as one epoch (E1; mid-point 26 Aug/08:43 UT). The second epoch consists of jointly analyzed data collected on 5-6 September (E2; mid-point 6 Sep/03:22 UT). The third epoch refers to observations done on 17 September (E3; start time 07:16 UT). NGC4993 flux densities (1 sigma uncertainties): E1: 0.56+/-0.04 mJy (synthesized beam 14.5"x7.8") E2: 0.58+/-0.05 mJy (synthesized beam 11.8"x6.3") E3: 0.61+/-0.03 mJy (synthesized beam 10.4"x4.8") SSS17a flux density limits (3 sigma): E1: <70 uJy E2: <75 uJy E3: <60 uJy We thank the SKA South Africa team for enabling these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21935 SUBJECT: LIGO/VIRGO G298048: VLA detection of the radio counterpart at 6 GHz DATE: 17/09/27 19:03:46 GMT FROM: Kate Alexander at Harvard U K. D. Alexander (Harvard), W. Fong (Northwestern), P. K. G. Williams, E. Berger (Harvard), and R. Margutti (Northwestern) report: We report continued radio monitoring of LIGO/VIRGO G298048 with the Karl G. Jansky Very Large Array (PI: Alexander, Program 17A-231). Our most recent observations started on 2017 September 25.703 UT, or 39.2 days post-trigger (LVC et al., GCN 21509), at a mean frequency of 6 GHz. We clearly detect the radio counterpart (Hallinan et al., GCN 21929) at ~5-sigma significance at a brightness comparable to the limit of our previous VLA observations. Further observations are planned. We thank the VLA staff for their assistance in scheduling and executing these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21939 SUBJECT: LIGO/Virgo G298048: Further European VLBI Network (EVN) observations of SSS17a DATE: 17/09/28 10:35:27 GMT FROM: Zsolt Paragi at Euro VLBI Zsolt Paragi (JIVE), Jun Yang (OSO), Benito Marcote (JIVE) et al. for the Euro VLBI team Continuing our efforts (LVC GCN 20981, 21804) to detect radio emission from SSS17a (Coulter et al. LVC GCN 21529) on milliarcsecond scales, we observed the transient at 5 GHz with the European VLBI Network between 10:00—14:30 UT on 20 September 2017. The 5 sigma upper limit around the HST/Gaia position (Adams, Kasliwal & Blagorodnova, LVC GCN 21816) is 140 microJy/beam. Further observations are planned. Euro VLBI team members: Ivan Agudo (IAA Granada) Tao An (Shanghai Astronomical Observatory) Philippe Bacon (APC Université Paris Diderot) Rob Beswick (JBO-Manchester University) Carolina Casadio (MPIfR-Bonn) Eric Chassande-Mottin (APC Université Paris Diderot) Sándor Frey (Konkoly Observatory) Marcello Giroletti (IRA-INAF) Peter Jonker (SRON) Mark Kettenis (JIVE) Benito Marcote (JIVE) Javier Moldon (JBO-Manchester University) Zsolt Paragi (JIVE) Arpad Szomoru (JIVE) Huib van Langevelde (JIVE) Jun Yang (Onsala Space Observatory) The EVN is a joint facility of independent European, African, Asian, and North American radio astronomy institutes. Scientific results from data presented in this publication are derived from the following EVN project code: RP029. -- Zsolt Paragi Head of User Support Joint Institute for VLBI ERIC (JIVE) Web: http://www.jive.eu Oude Hoogeveensedijk 4 Phone: +31 (0)521-596-536 7991 PD Dwingeloo Mobile: +31 (0)629-034-718 the Netherlands Fax: +31 (0)521-596-539 //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21940 SUBJECT: LIGO/Virgo G298048: Record of all e-MERLIN results to date on SSS17a DATE: 17/09/28 11:12:37 GMT FROM: Zsolt Paragi at Euro VLBI Javier Moldon, Rob Beswick (JBCA, The University of Manchester) et al. for the EuroVLBI team We conducted a total of 22 e-MERLIN observations of SSS17a (Coulter et al. LVC GCN 21529) from Aug 23 to Sep 22, 2017 for about 5 hours per run. The observing frequency was centred at 5 GHz with a bandwidth of 512 MHz. The average synthesized beam size was about 200 mas x 30 mas at a position angle of about 0 deg. There are no significant detections in individual runs or in different combinations of adjacent runs coincident with the position of the transient. The 3-sigma upper limits in microJy/beam are listed below (first six runs were already reported in LVC GCN 21804). UTC date and times refer to the middle of the experiments: run00 2017-08-23 15:36:28 110 run01 2017-08-24 15:33:42 90 run02 2017-08-25 15:30:26 97 run03 2017-08-26 15:30:26 112 run04 2017-08-27 15:30:22 87 run05 2017-08-28 15:30:26 82 run06 2017-08-31 15:01:26 109 run07 2017-09-01 15:01:26 114 run08 2017-09-02 15:04:42 144 run09 2017-09-03 15:01:26 166 run10 2017-09-04 15:01:26 147 run11 2017-09-05 15:31:29 162 run12 2017-09-10 14:54:42 126 run13 2017-09-11 14:44:42 151 run14 2017-09-12 14:03:28 113 run15 2017-09-14 13:26:42 147 run16 2017-09-15 14:03:28 106 run17 2017-09-16 14:03:28 118 run18 2017-09-17 14:03:28 111 run19 2017-09-18 14:03:28 111 run20 2017-09-21 14:18:28 132 run21 2017-09-22 13:34:42 121 Additional observations are planned with e-MERLIN to continue the monitoring of the transient source. Euro VLBI team members: Ivan Agudo (IAA Granada) Tao An (Shanghai Astronomical Observatory) Philippe Bacon (APC Université Paris Diderot) Rob Beswick (JBO-Manchester University) Carolina Casadio (MPIfR-Bonn) Eric Chassande-Mottin (APC Université Paris Diderot) Sándor Frey (Konkoly Observatory) Marcello Giroletti (IRA-INAF) Peter Jonker (SRON) Mark Kettenis (JIVE) Benito Marcote (JIVE) Javier Moldon (JBO-Manchester University) Zsolt Paragi (JIVE) Arpad Szomoru (JIVE) Huib van Langevelde (JIVE) Jun Yang (Onsala Space Observatory) e-MERLIN is a National Facility operated by the University of Manchester at Jodrell Bank Observatory on behalf of STFC. -- Zsolt Paragi Head of User Support Joint Institute for VLBI ERIC (JIVE) Web: http://www.jive.eu Oude Hoogeveensedijk 4 Phone: +31 (0)521-596-536 7991 PD Dwingeloo Mobile: +31 (0)629-034-718 the Netherlands Fax: +31 (0)521-596-539 //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21975 SUBJECT: LIGO/Virgo G298048: LWA radio observations DATE: 17/10/06 15:41:34 GMT FROM: Christopher League at FRBSG T. Callister (Caltech), J. Dowell (U New Mexico), J. Kanner (Caltech), M. Kavic (LIU Brooklyn), C. League (LIU Brooklyn), P. Shawhan (U Maryland), J. Simonetti (Virginia Tech), G. Taylor (U New Mexico), J. Tsai (Virginia Tech), C. Yancey (U Maryland) As previously reported (GCN 21680, GCN 21848), the Long Wavelength Array (LWA1, located west of Socorro, New Mexico) followed up on G298048 on 17 August and 24 August, observing with 4 beams: one centered on NGC 4993, one including it off-center, and two nearby that exclude the source. After including observations from an additional epoch (30 August at 19:50 UTC, two weeks after the GW event), and further analysis, we have concluded that the detection reported earlier (GCN 21848) is not statistically significant. We now set 3-sigma upper limits to the appearance of a radio source in an LWA1 beam centered on NGC 4993, about 8 hours after the GW event, as ~200 Jy at 25 MHz and ~100 Jy at 45 MHz. A publication describing these limits and our analysis is in preparation. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21982 SUBJECT: LIGO/Virgo G298048: Mid-Infrared Spitzer/IRAC Observations at 3.6 and 4.5 microns DATE: 17/10/10 13:57:54 GMT FROM: Mansi M. Kasliwal at Caltech R. M. Lau (Caltech), E. O. Ofek (Weizmann) and M. M. Kasliwal (Caltech) report on behalf of the Global Relay of Observatories Watching Transients Happen (GROWTH) collaboration: On 2017 Sept 29.86 UT, the Spitzer space telescope took deep mid-infrared observations at the position of SSS17a (Coulter et al. LVC GCN 21529) with Channel 1 (3.6 microns) and Channel 2 (4.5 microns) of the Infrared Array Camera (IRAC). We conducted a preliminary analysis of the IRAC Basic Calibrated Data (BCD), including both a median filter subtraction and ZOGY image subtraction to remove the extended emission from the host galaxy NGC 4993. We find possible, marginal evidence for excess emission at the position of SSS17a at 4.5um. We are continuing monitoring with Spitzer/IRAC. We thank the Spitzer Space Telescope team, in particular, Tom Soifer and Nancy Silbermann, for the rapid review and scheduling of these DDT observations (PI Kasliwal). The Spitzer Space Telescope is operated by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 21983 SUBJECT: LIGO/Virgo G298048/GW170817: updated localization from parameter estimation DATE: 17/10/10 16:16:03 GMT FROM: Leo Singer at NASA/GSFC The LIGO Scientific Collaboration and the Virgo Collaboration report: We have re-analysed offline noise-subtracted data for the LIGO Hanford Observatory (H), LIGO Livingston Observatory (L), and Virgo (V) detectors around the time of the binary neutron star merger event G298048 / GW170817 (GCNs 21505, 21509, 21510, 21513, 21527) taking into account our most up-to-date understanding of both calibration and waveform modelling uncertainties. Parameter estimation has been performed using LALInference (Veitch et al., PRD 91, 042003) and a new sky map, LALInference_v2.fits.gz, is available for retrieval from the GraceDB event page: https://gracedb.ligo.org/events/G298048 The 50% and 90% credible regions span about 8 and 28 square degrees, respectively. This is the preferred sky map at this time, and the version that will appear in LVC 2017 (Physical Review Letters, accepted). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22201 SUBJECT: LIGO/Virgo G298048: Late-time detection of the X-ray afterglow with Chandra DATE: 17/12/07 17:34:57 GMT FROM: Eleonora Troja at GSFC E. Troja (UMD/GSFC), L. Piro (INAF/IAPS), G. Ryan (UMD), H. van Eeerten (U. Bath), T. Sakamoto (AGU), and S. B. Cenko (NASA/GSFC) report: The Chandra X-ray Observatory re-observed the field of GW170817/AT2017gfo (PI: B. Wilkes) starting on 2017-12-03 (~109 days after the LVC trigger) for a total exposure of 74 ks. A second shorter observation was performed on 2017-12-06 for a total exposure of 25 ks. Our preliminary analysis of the data clearly detects the X-ray counterpart of AT2017gfo at a flux level of ~1.5E-14 erg/cm^2/s (0.5-8.0 keV). The observed value is three times higher than the flux measured at earlier times (~5E-15 erg/cm^2/s at 15 days; Troja, E., et al. 2017, Nature, 551, 71) and implies a continued rise of the X-ray afterglow. We do not measure any significant spectral variation between these observations and our observations at earlier times. This behavior is hard to reconcile with the simple top-hat jet model and suggests a more complex structure of the GRB jet. We thank Belinda Wilkes, Andrea Prestwich and the entire Chandra for performing these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22203 SUBJECT: LIGO/Virgo GW170817: Chandra X-ray brightening of the counterpart 108 days since merger DATE: 17/12/07 18:04:04 GMT FROM: Raffaella Margutti at Northwestern U R. Margutti, W. Fong (Northwestern), T. Eftekhari, K. Alexander, E. Berger (Harvard), R. Chornock (Ohio University) report: The Chandra X-ray Observatory (CXO) started observing GW170817 on 2017 December 3 at 01:38:45UT for a total of 74.09 ksec (obs ID 20860, PI Wilkes). At the position of the electromagnetic counterpart, an X-ray source is clearly detected with a significance of ~33-sigma (RA = 13:09:48.090, Dec = -23:22:52.87, J2000), with a net count-rate of 1.47e-3 cps (0.5-8 keV). The CXO observed the field for an additional 24.74 ksec starting on 2017 December 6 at 10:43:31UT (obs ID 20861, PI Wilkes). The X-ray source is still detected with a significance of ~15-sigma with a net count-rate of 1.41e-3 cps (0.5-8 keV). The joint spectrum can be fit with an absorbed power-law spectral model with photon index Gamma= 1.50 +\-0.16 (1 sigma c.l.). We find no evidence for intrinsic neutral hydrogen absorption in addition to the Galactic value (NH_MW=0.0784e22 cm-2, Kalberla et al., 2005) and place a 3 sigma upper limit of NHint<0.7e22 cm-2. These properties are consistent with the X-ray spectral properties of GW170817 at t<15 days inferred by Margutti et al., 2017 and Troja et al., 2017. Based on our best fitting spectral parameters, the 0.3-10 keV unabsorbed flux is 2.3e-14 erg/s/cm^2, indicating a substantial brightening of the X-ray source during the last ~90 days, in agreement with the results from Troja et al., GCN 22201. A comparison with radio observations acquired 93 days since merger (Mooley et al., 2017) indicates a spectral slope beta~-0.6 of the Fnu ~nu^-beta spectrum, similar to the radio-to-Xray spectrum of GW170817 before Sun block (Alexander et al., 2017; Margutti et al., 2017; Troja et al., 2017; Haggard et al., 2017; Hallinan et al., 2017; Mooley et al., 2017). This result suggests negligible spectral evolution of GW170817 in the last 90 days, and that the radio and X-ray emission continue to represent the same emission component. Based on this spectrum, we expect GW170817 to be detectable at optical-NIR wavelengths at approximately 26.5 AB magnitude. We thank Belinda Wilkes and the entire CXO team for approving these DDT requests and making these observations possible. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22206 SUBJECT: LIGO/Virgo G298048: Brightening X-ray Emission from GW170817/GRB170817A/SSS17a DATE: 17/12/07 22:11:17 GMT FROM: Phil Evans at U of Leicester Daryl Haggard, John J. Ruan, Melania Nynka (McGill/MSI), Vicky Kalogera (Northwestern/CIERA), and Phil Evans (Leicester) report: We have performed a detailed analysis of new Chandra X-ray observations of GW170817 obtained via Chandra Director's Discretionary Time (PI: Wilkes, Program Number 18408601). The X-ray counterpart to GW170817/GRB170817A/SSS17a is clearly detected in the new observations. This program acquired two exposures of GRB170817A: (1) a 74.09 ks exposure (ObsID 20860) beginning at 2017 December 2.08 UT, approximately 108 days post-burst, and (2) a 24.74 ks exposure (ObsID 20861) beginning at 2017 December 6.45 UT, approximately 111 days post-burst. Since the two new exposures are close in time and the X-ray emission of GRB170817A is not expected to vary significantly over ~4 day timescales, we co-add the two data sets into one 98.83 ks exposure at 109.2 days post-burst. We perform spectral extractions assuming an absorbed power-law spectral model with fixed NH = 7.5e20 cm^−2 and find that the X-ray flux of GRB170817A has an absorbed flux of f(0.3−8 keV) = 1.58e−14 +/- 0.14 erg s^−1 cm^−2 (Gamma = 1.62 +/- 0.27) at 109.2 days post-burst, which corresponds to an unabsorbed luminosity of L(0.3−10 keV) = 42.5e38 +/- 3.7 erg s^−1 (see also Troja et al. GCN 22201 and Margutti et al. GCN 22203). This represents significant X-ray brightening compared to Chandra observations at 15.6 days post-burst, for which we find an absorbed flux of f(0.3−8 keV) = 0.36e−14 +/- 0.1 erg s^−1 cm^−2 (Gamma = 2.4 +/- 0.8) and an unabsorbed luminosity of L(0.3−10 keV) = 10.4e38 +/- 2.0 erg s^−1 (Haggard et al. 2017). We also examine the three previously-detected X-ray sources CXOU J130948, CXOU 130946, and the host galaxy NGC 4993. The fluxes of CXOU 130946 and the host-galaxy NGC 4993 are consistent with our previous deep Chandra observations, while CXOU J130948 appears to be variable in X-rays (Margutti et al. 2017; Haggard et al. 2017). The origin of the X-ray emission from the NS-NS coalescence GW170817/GRB170817A is an important diagnostic for all post-merger interpretations, and different scenarios predict distinct evolution in its X-ray light curve. These observations support scenarios in which the X-ray and radio emission share a common origin, i.e., the X-ray light curve is consistent with outflow models which may be either a cocoon shocked by the jet or dynamical ejecta from the merger. Further deep X-ray monitoring can place powerful constraints on the physical parameters of these models. The X-ray brightening strengthens the argument that simple top-hat jet models are not consistent with the latest observations. However, more advanced models of structured jets with off-axis viewing angles should be pursued and cannot yet be ruled out. We thank Belinda Wilkes and the Chandra scheduling, data processing, and archive teams for making these observations possible. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22207 SUBJECT: LIGO/Virgo GW170817: Further Hubble Space Telescope observations DATE: 17/12/07 22:47:21 GMT FROM: Andrew Levan at U.of Leicester A.J. Levan, J.D. Lyman (U. Warwick), N.R. Tanvir (U. Leicester), I. Mandel (U. Birmingham), J. Hjorth (DARK/NBI), A.S. Fruchter, T. Kangas (STScI), B. Gompertz, K. Wiersema, D. Steeghs (U. Warwick), S. Rosswog (Stockholm) report on behalf of a larger collaboration: "We obtained further observations of the counterpart of GW170817 with the Hubble Space Telescope. Observations took place on 6 Dec 2017 and utilised both optical (F606W, F814W) and infrared (F140W,F160W) filters. At the location of the transient we recover the source in both optical filters, but do not detect it in the infrared, where the background from the galaxy is higher. The measured magnitudes of the source in the optical bands are broadly consistent with the extrapolation from the 93 day radio epoch (Mooley et al. 2017 arXiv 1711.11573) to the near contemporaneous observations with Chandra (Troja et al. 2017 GCN 22201, Margutti et al. 2017 GCN 22202). We thank the staff of STScI for their excellent support with these observations." //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22211 SUBJECT: LIGO/Virgo GW170817: X-ray observations confirm prediction made from radio data DATE: 17/12/08 21:30:16 GMT FROM: Kunal Mooley at Oxford U K. P. Mooley (Oxford, NRAO/Caltech) et al. report The X-ray flux of GW170817 on December 03-06 (reported by Troja et al. 2017, GCN 22201; Margutti et al. 2017, GCN 22203, Haggard et al. 2017, GCN 22206 based on the Chandra observations) is exactly as predicted last week by Mooley et al. 2017 (http://arxiv.org/abs/1711.11573) based on radio spectral indices. This suggests that the radio and X-ray emission both arise from a mildly relativistic wide-angle outflow, consistent with the cocoon model (see also Gottlieb et al. 2017, Hallinan et al. 2017, Kasliwal et al. 2017). A relativistic jet core, if it exists, is either too weak (having a sub-dominant contribution to the radio light curve early on) or too strong (such that its electromagnetic signatures will be observed in the future). See Mooley et al. 2017 for details. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22368 SUBJECT: LIGO/Virgo G298048 GRAWITA: VST-ESO PARANAL follow up of AT2017gfo DATE: 18/01/24 08:46:57 GMT FROM: Aniello Grado at INAF-OAC A. Grado (INAF-OAC), E. Cappellaro (INAF-OAPD), F. Getman (INAF-OAC), L. Limatola (INAF-OAC), S. Yang (INAF-OAPD), M. Branchesi (GSSI), S. Covino (INAF-OAB), P. D'Avanzo (INAF-OAB), M. Della Valle (INAF-OAC), A. Melandri (INAF-OAB), L. Amati (INAF-OAS), S. Ascenzi (INAF-OAR), S. Benetti (INAF-OAPD), M.T. Botticella (INAF-OAC), G. Greco (Urbino University/INFN Firenze), L. Nicastro (INAF-OAS), E. Palazzi (INAF-OAS), E. Pian (INAF-OAS), S. Piranomonte (INAF-OAR), A. Rossi (INAF-OAS), G. Stratta (Urbino University/INFN Firenze), G. Tagliaferri (INAF-OAB), L . Tomasella (INAF-OAPD), E. Brocato (INAF-OAR) on behalf of GRavitational Wave Inaf TeAm. Observations pointed at the position of AT2017gfo of the skymap of the Advanced LIGO and Virgo trigger G298048 (LVC GCN Circ. 21509, 21513) using the VLT Survey Telescope (VST - Proposal ID ESO 0100.D-0022) at ESO-Paranal equipped with OMEGACAM (FOV=1 square degree). The images were acquired with the g_SDSS, r_SDSS, filters for a total exposure of 5400s in each band. The observations were executed in the nights 2018-01-05, 2018-01-18 and 2018-01-19, starting at 2018-01-05T 06:57:00.057 UTC and finishing at 2018-01-19T 06:55:22.862 UTC. The median FWHM and the 50% completeness magnitudes are 0.91", 0.92" and 25.0 and 24.5 AB mags for the g_ssds and r_sdss bands respectively. No source is visible at the GW optical counterpart coordinates RA=13:09:48.09 DEC=-23:22:53.35. We acknowledge excellent support from the ESO User Support Department and from ESO observing staff in Paranal. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22371 SUBJECT: LIGO/Virgo GW170817: Chandra X-ray Emission Continues to Rise ~156 Days Post-Merger DATE: 18/01/29 19:21:22 GMT FROM: Daryl Haggard at McGill U Daryl Haggard, Melania Nynka, John J. Ruan (McGill/MSI), Phil Evans (Leicester), and Vicky Kalogera (Northwestern/CIERA) report: We have obtained new X-ray observations of GW170817 via Chandra Director's Discretionary Time (PI: Wilkes, Program Number 19408607). The X-ray counterpart to GW170817/GRB170817A/SSS17a continues to be detected and the X-ray emission continues to brighten approximately 156 days after the neutron star merger. This contradicts previous claims of the X-ray fading of GW170817 in XMM-Newton observations at 135 days (D'Avanzo et al. 2018, arXiv: 1801.06164). This new Chandra program acquired several exposures of GRB170817A: ObsID, ExpTime, StartDate, Days Post-Burst ----- ------- --------- --------------- 20936 31.75 ks 2018-01-17 21:55:17 153.5 days 20938 15.86 ks 2018-01-21 13:45:18 157.1 days 20939 22.25 ks 2018-01-24 08:18:48 159.9 days Since these new Chandra exposures are close in time and the X-ray emission of GRB170817A is not expected to vary significantly over <10 day timescales, we co-add these three data sets into one 69.86 ks exposure at 156.4 days post-burst. We perform spectral extractions assuming an absorbed power-law spectral model with fixed NH = 7.5e20 cm^2 and find that the X-ray flux of GRB170817A has an absorbed flux of f(0.38 keV) = 1.93(+0.39/-0.32)e14 erg s^1 cm^2 (with Gamma ~ 1.67) at 156.4 days post-burst, which corresponds to an unabsorbed luminosity of L(0.310 keV) = 5.23(+1.30/-0.95)e39 erg s^1 (assuming a luminosity distance of 42.5 Mpc). This represents continued X-ray brightening compared to Chandra observations at 15.6 and 109.2 days post-burst, for which we find an absorbed flux of f(0.38 keV) = 0.36(+0.1/-0.07)e14 erg s^1 cm^2 (with Gamma = 2.4 +/- 0.8, unabsorbed L(0.310 keV) = 10.4(+2.0/-1.6)e38 erg s^1; Haggard et al. 2017) and f(0.38 keV) = 1.58(+0.14/-0.13)e14 erg s^1 cm^2 (with Gamma = 1.6 +/- 0.3, unabsorbed L(0.310 keV) = 42.5(+3.7/-3.5)e38 erg s^1; Ruan et al. 2018), respectively. Our findings here contradict recent reports of dimming in the X-ray flux from XMM Newton at 135 days (D'Avanzo et al. 2018), which was reported to be 2.1(+0.7/-0.5)e-15 erg s^1 cm^2 (0.3-10 keV unabsorbed). However, this reported flux value is a typo, and should be 2.1(+0.7/-0.5)e-14 erg s^1 cm^2 (DAvanzo 2018, private communication). Taking this corrected flux and rescaling to a 0.3-8 keV absorbed flux for comparison to the previous Chandra measurements above gives 1.67(+0.87/-0.64)e-14 erg s^1 cm^2. Thus, the recent X-ray data at 15.6 days (Chandra), 109.2 days (Chandra), 135 days (XMM), and 156.4 days (Chandra) are all consistent with continued X-ray brightening. We provide a light curve table summarizing these measurements: Days, Telescope, Flux* (0.3-8 abs), Ref ---- --------- ---------------- --- 15.6 Chandra 0.36(+0.10/-0.07)e14 Haggard et al. (2017) 109.2 Chandra 1.58(+0.14/-0.13)e14 Ruan et al. (2018) 135 XMM 1.67(+0.87/-0.64)e-14 D'Avanzo et al. (2018) 156.4 Chandra 1.93(+0.39/-0.32)e-14 This work *Flux units: erg s^1 cm^2; all uncertainties are 90% confidence interval Current post-merger models suggest that the origin of the X-rays could be afterglow emission from either a mildly-relativistic cocoon or a structured jet. For a cocoon, the continued rise of X-ray emission suggest that the cocoon has not yet reached a deceleration phase. For a structured jet, the rising X-ray emission suggest emission from the jet core has not yet entered the observed line of sight. Continued monitoring of GW170817 will be critical for discriminating between these and other models. Note that another ~30 ks of Chandra observations during this same time interval are forthcoming. We thank Belinda Wilkes and the Chandra scheduling, data processing, and archive teams for making these observations possible. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22372 SUBJECT: GW170817/GRB170817A: Preliminary results of Chandra monitoring DATE: 18/01/29 20:42:49 GMT FROM: Eleonora Troja at GSFC E. Troja (UMD/GSFC) and L. Piro (INAF/IAPS) report on behalf of a larger collaboration: The Chandra X-ray Observatory re-observed the field of GW170817 starting on January 17th, 2018, and performed five short exposures observations as part of its on-going monitoring program (PI: Wilkes). Only three of these exposures (ObsID: 20936, 20938, 20939) are currently archived and available to the public. Here we report the preliminary findings from these observations. The X-ray afterglow is detected with high significance in all the exposures at an average count rate of 0.0016 cts/s in the 0.5-8.0 keV energy band. A preliminary inspection of the hardness ratio does not show any significant spectral variation. Therefore, we perform a spectral analysis using an absorbed power-law model with absorption column fixed at the Galactic value of 7.5E20 cm^-2 and a photon index Gamma=1.575 as derived from our broadband analysis (Troja et al. 2018, arXiv:1801.06516). We derive an unabsorbed X-ray flux of (3.2 +/- 0.3)E-14 erg/cm2/s in the 0.3-10 keV energy band. The quoted error is at the 68% confidence level. This new measurement is higher than the value measured by Chandra at ~110 days (~2.5E-14 erg/cm2/s, Troja et al. 2018), and higher than the value measured by XMM-Newton at ~135 days (D'Avanzo et al., 2018). The latest measurement is consistent with a rising afterglow with F~t^0.8, although, within the errors, a slow turn-over of the X-ray light curve cannot be excluded. Further analysis is on-going. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22374 SUBJECT: GW170817/GRB170817A: Updated results from the full Chandra dataset DATE: 18/01/30 13:00:12 GMT FROM: Eleonora Troja at GSFC E. Troja (UMD/GSFC) and L. Piro (INAF/IAPS) report on behalf of a larger collaboration: We analyzed the full set of five observations of GW170817 performed by the Chandra X-ray Observatory between January 17th and January 28th, 2018, i.e. ~153 and ~164 days after the merger. A log of observations is reported below: ObsID Exposure [ks] 0.5-8.0 keV count rate [cts/s] 20936 31.75 0.0018 +/- 0.0002 20937 20.77 0.0014 +/- 0.0003 20938 15.86 0.0019 +/- 0.0003 20939 22.25 0.0011 +/- 0.0002 20945 14.22 0.0010 +/- 0.0003 The average net count-rate is 0.00148 +/- 0.00011 cts/s, consistent with the value of 0.00145 +/- 0.00014 observed at 110 days (Troja et al. 2018, arXiv:1801.06516). The average spectrum, obtained by coadding the five exposures, is well described by an absorbed power-law model with N_H=7.5E20 cm^-2 and photon index Gamma=1.65+/-0.16 (68% c.l.), consistent with the value derived from the broadband spectrum at earlier times (Troja et al. 2018, arXiv:1801.06516). Based on this new analysis, we estimate an unabsorbed X-ray flux of (2.6 +/- 0.3)E-14 erg/cm2/s (68% c.l.) in the 0.3-10 keV band, consistent with the X-ray flux measured at 110 days. Our results do not support the claim of a decreasing X-ray flux, as suggested by D'Avanzo et al. (2018, arXiv:1801.06164), and are consistent either with a slowly rising afterglow or a slow turn-over of the X-ray light curve expected when the afterglow reaches its peak (e.g. Lazzati et al. 2017, arXiv:1712.03237; Troja et al. 2018, arXiv:1801.06516). We note that the X-ray afterglow displays a marginal level of variability on timescales of a few days, being the count-rate from the last two exposures (20939,20945) consistently lower. The spectrum from these two observations is characterized by a photon index Gamma= 1.9 +/- 0.3 (68% c. l.), slightly softer than the value measured in the first three exposures (20936,20937, and 20938) Gamma = 1.59+/-0.17 (68% c. l.), yet consistent within the large uncertainties. The lower count-rate and soft spectral shape could be indicative of the cooling frequency entering the X-ray band, although the limited statistics prevent us to draw any firm conclusion. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22692 SUBJECT: Chandra observations of GW170817 260 days since merger: first statistically significant evidence for an X-ray decay DATE: 18/05/08 01:44:24 GMT FROM: Kate Alexander at Harvard A. Hajela (Northwestern/CIERA), K. D. Alexander, T. Eftekhari (Harvard/CfA), R. Margutti, W. Fong (Northwestern/CIERA), E. Berger (Harvard/CfA) report "The Chandra X-ray Observatory started another round of follow-up observations of GW170817. The first observation (ID 21080) was taken on May 03, 2018 at 10:41:26 UT (t ~ 259 d after merger) for a total exposure time of 50.8 ks (PI Wilkes; program 19408644). We find that an X-ray source is detected at the location of GW170817 with a count-rate of (7.7 +/- 1.3)e-4 cts/s (0.5 - 8 keV) and 13.8-sigma significance. We modeled the spectrum with an absorbed simple power-law and find a best-fitting photon index, Gamma = 1.4 +/- 0.3 and no evidence for intrinsic absorption. The galactic neutral hydrogen column density in the direction of the transient is, N_H = 7.8E+20cm-2 (Kalberla et al., 2005). For these parameters, the unabsorbed flux is (1.3 +/- 0.3)e-14 ergs cm-2 s-1 (0.3 - 10 keV). A second observation (ID 21090) was acquired on May 05, 2018 at 01:25:30 UT (~ 261 days after merger) for a total exposure time of 46.0 ks. GW170817 is detected with 14.8-sigma significance and a count-rate of (8.3 +/- 1.4)e-4 cts/s (0.5 - 8 keV). The best-fitting photon-index is Gamma = 1.3 +/- 0.3. The corresponding unabsorbed flux is (1.5 +0.5/-0.3) e-14 ergs cm-2 s-1 (0.3 - 10 keV). The best fitting photon index from a joint spectral fit is Gamma = 1.43 +/- 0.15, consistent with the photon index measured at ~160 days. We conclude that there is no evidence for the passage of the synchrotron cooling frequency through the Chandra band. The total 0.5-8 keV count-rate inferred from the two observations is (8.0+/-0.9)e-4 cts/s. The X-ray source shows significant fading compared to the previous epoch at ~160 days (inferred rate of (1.50 +\-0.12)e-3 cts/s, Margutti et al., 2018). Applying a simple binomial test, we find that the detected fading is significant at a level > 4 sigma. We can thus reject the hypothesis of a random fluctuation of the X-ray count-rate, and conclude that these Chandra observations provide the first statistically significant evidence for a decaying X-ray emission from GW170817. We thank the entire Chandra team for making these observations possible." //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22693 SUBJECT: Chandra observations of GW170817 reveal a fading afterglow DATE: 18/05/08 03:59:58 GMT FROM: Eleonora Troja at GSFC E. Troja (UMD/GSFC), L. Piro (IAPS/INAF), G. Ryan (UMD) report on behalf of a larger collaboration: The Chandra X-ray Observatory re-observed the field of GW170817 starting on May 3rd, 2018 as part of its on-going monitoring program (PI: Wilkes). Observations were split into two exposures of 50.7 ks and 46 ks, respectively. The X-ray afterglow is significantly detected at an average level of (8.5 +/- 1.4)E-04 cts/s, well below the value (14.8 +/- 1.1)E-04 cts/s measured at ~160 d after the merger (Troja & Piro, GCN Circ. 22374; Troja et al. 2018). The spectrum is well described by an absorbed power-law model with photon index 1.5 +/- 0.2, consistent with the value of 1.575 derived at earlier times from the broadband spectrum. By using this value we derive an unabsorbed X-ray flux of (1.4 +/- 0.2)E-14 erg/cm2/s at 260 days after the merger. A comparison with the afterglow models derived in Troja et al. (2018) is shown at this link: https://www.astro.umd.edu/~gsryan/GW170817/xray.png This new X-ray observation supports earlier claims (D'Avanzo et al. 2018; Dobie et al. 2018) that the afterglow entered its post-peak decay phase. However, no clear distinction between the competing models is possible. Further observations are critical to probe the structure of the relativistic outflow. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22763 SUBJECT: GW170817/GRB170817A: LBT optical detection DATE: 18/06/05 14:03:37 GMT FROM: Andrea Rossi at INAF A. Rossi (INAF-OAS), M. Cantiello (INAF-OA Abruzzo) V. Testa, D. Paris (INAF-OAR), A. Melandri, S. Covino, O. S. Salafia, P. D'Avanzo, S. Campana (INAF-OAB), L. Nicastro, E. Palazzi, F. Cusano (INAF-OAS), G. Stratta (Urbino University/INFN Firenze), R. Carini, S. Piranomonte, E. Brocato (INAF-OAR), V. D'Elia (ASDC), and M. Branchesi (GSSI) report on behalf of the GRAWITA collaboration and its partners: We observed the optical counterpart of GRB 170817A (Kienlin et al., GCN 21520) associated to GW 170817 (LVC GCN Circ. 21509, 21513) with the LBC imager mounted on the Large Binocular Telescope (Mt Graham, AZ, USA). Observations were performed in the r-sloan filter on 2018-01-23, i.e., ~160 days after the GW/GRB trigger. At the location of the optical transient (e.g., Coulter et al., GCN 21529; Adams et al., 21816) we detect the optical afterglow of GRB 170817A with magnitude r-sloan=26.2+-0.4, calibrated against Pan-STARRS field stars. Image analysis was performed after preliminary removal of an elliptical model of the underlying host galaxy from each single frame. However, some residual emission is left which contributes for ~0.2 mags to the uncertainty of the photometry. Our detection is the first one from a ground-based optical telescope. It is in agreement with a turnover/flattening in the optical light curve of GW 170817/GRB 170817A as inferred by Alexander at al. 2018 (arXiv:1805.02870) and with the overall flattening/declining temporal evolution observed in the X-ray and radio bands (D'Avanzo et al. 2018, A&A, 613 L1; Hajela et al. GCN Circ. 22692; Troja et al. GCN Circ. 22693; Dobie et al. arXiv:1803.06853; Alexander at al. 2018; arXiv:1805.02870). We acknowledge the excellent support from the LBT staff in obtaining these observations. //////////////////////////////////////////////////////////////////////// ATEL #11037 ATEL #11037 Title: LIGO/Virgo GW170817: Chandra X-ray brightening of the counterpart 108 days since merger Author: R. Margutti, W. Fong (Northwestern), T. Eftekhari, K. Alexander, E. Berger (Harvard), R. Chornock (Ohio University) Queries: rafmargutti@gmail.com Posted: 7 Dec 2017; 18:00 UT Subjects:X-ray, Gravitational Waves The Chandra X-ray Observatory (CXO) started observing GW170817 on 2017 December 3 at 01:38:45UT for a total of 74.09 ksec (obs ID 20860, PI Wilkes). At the position of the electromagnetic counterpart, an X-ray source is clearly detected with a significance of ~33-sigma (RA = 13:09:48.090, Dec = -23:22:52.87, J2000), with a net count-rate of 1.47e-3 cps (0.5-8 keV). The CXO observed the field for an additional 24.74 ksec starting on 2017 December 6 at 10:43:31UT (obs ID 20861, PI Wilkes). The X-ray source is still detected with a significance of ~15-sigma with a net count-rate of 1.41e-3 cps (0.5-8 keV). The joint spectrum can be fit with an absorbed power-law spectral model with photon index Gamma= 1.50 +\-0.16 (1 sigma c.l.). We find no evidence for intrinsic neutral hydrogen absorption in addition to the Galactic value (NH_MW=0.0784e22 cm-2, Kalberla et al., 2005) and place a 3 sigma upper limit of NHint<0.7e22 cm-2. These properties are consistent with the X-ray spectral properties of GW170817 at t<15 days inferred by Margutti et al., 2017 and Troja et al., 2017. Based on our best fitting spectral parameters, the 0.3-10 keV unabsorbed flux is 2.3e-14 erg/s/cm^2, indicating a substantial brightening of the X-ray source during the last ~90 days, in agreement with the results from Troja et al., GCN 22201. A comparison with radio observations acquired 93 days since merger (Mooley et al., 2017) indicates a spectral slope beta~-0.6 of the Fnu ~nu^-beta spectrum, similar to the radio-to-Xray spectrum of GW170817 before Sun block (Alexander et al., 2017; Margutti et al., 2017; Troja et al., 2017; Haggard et al., 2017; Hallinan et al., 2017; Mooley et al., 2017). This result suggests negligible spectral evolution of GW170817 in the last 90 days, and that the radio and X-ray emission continue to represent the same emission component. Based on this spectrum, we expect GW170817 to be detectable at optical-NIR wavelengths at approximately 26.5 AB magnitude. We thank Belinda Wilkes and the entire CXO team for approving these DDT requests and making these observations possible. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 23137 SUBJECT: Chandra X-ray observations of GW170817 at 1 year post-merger: increasingly rapid fading DATE: 18/08/13 01:52:40 GMT FROM: Daryl Haggard at McGill U Daryl Haggard, Melania Nynka, and J. J. Ruan (McGill/MSI) report: We analyze new Chandra X-ray observations of neutron star merger GW170817 at 358.6 days post-merger, which now reveals fading at a t^-1.6 rate. Chandra obtained a 67.16 ks observation of GW170817 (ObsID: 21371, PI: Troja) on 10 August 2018, at 358.6 days post-merger. GW170817 is still clearly detected, and we measure a 0.5-8 keV count rate of 4.9 (+0.9/-0.9) cts/s. We extract and fit the X-ray spectrum assuming an absorbed power-law spectral model, with fixed NH = 7.5e20 cm^-2. We measure an absorbed flux of f(0.3-8 keV) = 6.3 (+3.8/-2.1) x10^-15 erg/s/cm^2 (90% c.l.) and photon index of Gamma = 1.6 (+1.3/-0.9), which corresponds to an unabsorbed luminosity of L(0.3-10 keV) = 1.7 (+1.1/-0.5) x10^39 erg/s assuming a luminosity distance of 42.5 Mpc. The previous Chandra observation at 260.0 days showed an absorbed flux of f(0.3-8 keV) = 1.09 (+0.24/-0.20) x10^-14 erg/s/cm^2 (Nynka et al. 2018). A power-law fit of this previous 260.0 day flux to the new 358.6 day flux reveals fading at a t^-1.6 rate. This is steeper than the t^-1.3 fading observed between 159.7 and 260.0 days post-merger, and thus the X-ray afterglow light curve is now fading more rapidly. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 23139 SUBJECT: LIGO/Virgo GW170817: A steep decline in the radio light curve and prediction for the X-rays DATE: 18/08/13 18:38:03 GMT FROM: Tara Murphy at U of Sydney D. Dobie (University of Sydney), K. Mooley (Caltech), T. Murphy (University of Sydney), D. Kaplan (UWM), E. Lenc (CSIRO), A. Corsi (TTU), D. Frail (NRAO), report on behalf of a larger collaboration Our continued observations of GW170817 with the ATCA and the VLA up to 300 days post-merger (Mooley et al. in prep) confirm the t^(-2) decline in the radio light curve initially reported in Mooley et al. 2018 (arXiv:1806.09693). Such a slope rules out a cocoon-dominated outflow at late times, and is instead the classic signature of a relativistic jet, consistent with the VLBI result from Mooley et al. 2018. The t^(-2) decline is also expected in the X-ray light curve, and may be confirmed by the Chandra observation carried out on 2018 Aug 10. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 23140 SUBJECT: Correction: Chandra X-ray observations of GW170817 at 1 year post-merger: increasingly rapid fading DATE: 18/08/14 15:42:03 GMT FROM: Daryl Haggard at McGill U Daryl Haggard, Melania Nynka, and J. J. Ruan (McGill/MSI) write: We correct a typo in GCN 23137: The 0.5-8 keV count rate measured in the 10 August 2018 Chandra observation of GW170817 should have read 4.9 (+0.9/-0.9) e-04 ct/s. All fluxes, photon indices, luminosities, light curve slopes, etc., reported in GCN 23137 are correct, and were derived from this correct count rate. GCN OPS NOTE(28aug18): Per author's request, the Subject-line was corrected with the proper referencing Subject-line.] //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 23986 SUBJECT: Chandra observations of GW170817 ~581 days since merger DATE: 19/03/22 16:02:48 GMT FROM: Raffaella Margutti at Northwestern U A. Hajela, R. Margutti, W. Fong , K. D. Alexander (Northwestern/CIERA), P. Blanchard (Harvard), R. Chornock (Ohio U.), D. Coppejans (Northwestern/CIERA), S. Gomez (Harvard), G. Hosseinzadeh (Harvard), G. Terreran (Northwestern/CIERA), A. Villar (Harvard) report: "We report the results from the first 36ks of Chandra observations of GW170817 (another ~ 64ks will be acquired in the next few days). Chandra started to observe GW170817 on 21 March 2019 at 07:44 UT (obsID 21322, Co-PIs Margutti and Fong; program 20500299). X-ray emission from GW170817 is detected at the level of ~3 sigma (assuming pure Poissonian statistics), with a 0.5-8 keV count-rate of (1.5 +\-0.7)e-4 c/s, and a total of ~5 net photons. Assuming a simple power-law spectrum with photon index Gamma=1.6 and no intrinsic absorption, as found in previous Chandra observations (e.g., Margutti et al., 2018; Alexander et al., 2018), the count-rate above translates into an unabsorbed flux of (2.3+\- 1.1)e-15 erg/s/cm2 (0.3-10 keV). The Galactic neutral hydrogen column density in the direction of the transient is N_H = 7.8e+20cm-2 (Kalberla et al., 2005). This flux measurement is consistent with the expectations from the fast decay of the emission from the jet (e.g., Margutti et al., 2018; Alexander et al., 2018; Wu et al., 2018). Fur(her Chandra observations are ongoing. We thank the entire Chandra team for making these observations possible." //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 23987 SUBJECT: Correction: Chandra observations of GW170817 ~581 days since merger DATE: 19/03/22 19:04:44 GMT FROM: Raffaella Margutti at Northwestern U A. Hajela, R. Margutti, W. Fong , K. D. Alexander (Northwestern/CIERA), E. Berger, P. Blanchard (Harvard), R. Chornock (Ohio U.), D. Coppejans (Northwestern/CIERA), S. Gomez (Harvard), G. Hosseinzadeh (Harvard), G. (erreran (Northwest)rn/CIERA), A. Villar (Harvard) report: "We report the results from the first 36ks of Chandra observations of GW170817 (another ~ 64ks will be acquired in the next few days). Chandra started to observe GW170817 on 21 March 2019 at 07:44 UT (obsID 21322, Co-PIs Margutti and Fong; program 20500299). X-ray emission from GW170817 is detected at the level of ~3 sigma (assuming pure Poissonian statistics), with a 0.5-8 keV count-rate of (1.5 +\-0.7)e-4 c/s, and a total of ~5 net photons. Assuming a simple power-law spectrum with photon index Gamma=1.6 and no intrinsic absorption, as found in previous Chandra observations (e.g., Margutti et al., 2018; Alexander et al., 2018), the count-rate above translates into an unabsorbed flux of (3.9+/-1.8)e-15 erg/s/cm2 (0.3-10 keV). The Galactic neutral hydrogen column density in the direction of the transient is N_H = 7.8e+20cm-2 (Kalberla et al., 2005). This flux measurement is consistent with the expectations from the fast decay of the emission from the jet (e.g., Margutti et al., 2018; Alexander et al., 2018; Wu et al., 2018). Further Chandra observations are ongoing. We thank the entire Chandra team for making these observations possible." //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 24000 SUBJECT: Further Chandra observations of GW170817 ~581-583 days since merger DATE: 19/03/25 03:12:22 GMT FROM: Aprajita Hajela at Northwestern U A. Hajela, R. Margutti, W. Fong , K. D. Alexander (Northwestern/CIERA), E. Berger, P. Blanchard (Harvard), R. Chornock (Ohio U.), D. Coppejans (Northwestern/CIERA), S. Gomez (Harvard), G. Hosseinzadeh (Harvard), G. Terreran (Northwestern/CIERA), A. Villar (Harvard) report: We initiated a series of Chandra X-ray observations of GW170817 at t~581 days since merger, for a total exposure time of 100 ks. The results from the first observation with the exposure time of ~36 ks is reported in Hajela et al. (GCN 23987). Here, we report on the remaining ~64ks of Chandra observations of GW170817 acquired starting on 22 March 2019 at 06:17 UT (obsID 22157, exposure time of ~38 ks) and 23 March 2019 at 23:52 UT (obsID 22158, exposure time of ~25 ks, PIs Margutti and Fong). X-ray emission from GW170817 is detected with a significance of >=3 sigma in each of the observations, with a total of ~6 and ~3 photons from the source in obsID 22157 and obsID 22158, respectively (0.5-8 keV energy range). Assuming a simple power-law spectral model with photon index Gamma = 1.6 and NHint = 0, as found in previous Chandra observations (e.g., Margutti et al., 2018; Alexander et al., 2018), we find an unabsorbed flux of (2.7 +\- 1.2)e-15 erg/s/cm2 and (6.3+\- 3.5)e-15 erg/s/cm2 for ObsID 22157 and 22158, respectively (0.3-10 keV). The Galactic neutral hydrogen column density in the direction of the transient is NH = 7.8e+20cm-2 (Kalberla et al., 2005). From a joint spectral fit of the three epochs of data (obsID 21322, 22157, and 22158) we find that the photon index is loosely constrained to Gamma=1.6 +/- 0.8 and there is no evidence for intrinsic absorption. For Gamma=1.6, and NHint=0, the joint fit of the entire 100ks of Chandra observations indicates an unabsorbed flux of (3.6 +/- 0.9)e-15 erg/s/cm2 (t~582 days since merger, 0.3-10 keV). We confirm that this flux measurement is consistent with the expectations from the fast decay of the emission from the jet (e.g., Margutti et al., 2018; Alexander et al., 2018; Wu et al., 2018). All fluxes reported are in the 0.3-10 keV energy range with 1-sigma uncertainties. We thank the entire Chandra team for making these observations possible. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25631 SUBJECT: Chandra observations of GW170817 ~740-743 days since merger DATE: 19/09/03 15:17:27 GMT FROM: Aprajita Hajela at Northwestern U A. Hajela, R. Margutti (Northwestern U.), T. Laskar (U Bath), D. Coppejans, G. Terreran, W. Fong, K. D. Alexander, A. Baldeschi, K. Paterson (Northwestern U.), E. Berger, P. K. Blanchard, T. Eftekhari, G. Hosseinzadeh, S. Gomez, V. A. Villar, P. K. G. Williams (Harvard U), M. Nicholl (U Edinburgh), R. Chornock (Ohio U), P. S. Cowperthwaite (Carnegie Observatories), D. Giannios (Purdue U.), A. MacFadyen (NYU), A. Kathirgamaraju (UC Berkeley) report: We report on Chandra observations of GW170817 acquired ~2 yrs after the binary neutron star merger. The Chandra X-ray Observatory started observing GW170817 August 27, 2019 at 14:16:40 UT (t ~ 740 d after merger) for an exposure time of 40.0 ks (PI Troja; program 20500691, observation ID 21372). Another two epochs of Chandra observations were acquired on August 29, 2019 at 13:46:01 UT (ID 22736) and on August 30, 2019 at 11:46:44 UT (ID 22737) for an exposure time of 33.6 ks and 25.3 ks, respectively. A preliminary reduction shows that GW170817 is detected in the merged exposure with a ~3 sigma significance and a net count-rate of (1.03 +\- 0.33)e-4 c/s (0.5-8 keV). Assuming negligible intrinsic absorption and a Galactic neutral hydrogen column density N_h = 7.8E+20cm-2 (Kalberla et al., 2005), we infer a best-fit photon index Gamma=1.0+/-1.3 and an unabsorbed flux of ~3e-15 erg/s/cm2 (0.3-10 keV). The photon index is loosely constrained by the observations and we therefore adopt the best-fit photon index from the entire Chandra data set acquired in the first two years of observations of GW170817 (Gamma=1.6) for the spectral calibration. We find an unabsorbed flux of (2.9 +\- 1.0)e-15 erg/s/cm2. These results are consistent within the uncertainties with the extrapolation of the off-axis structured jet model by Wu & MacFadyen (ApJ, 869, 55) at the current epoch. We thank the entire Chandra team for making these observations possible. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 27357 SUBJECT: Chandra observations of GW170817 ~ 2.5 years since merger (epoch 1 of 4) DATE: 20/03/11 00:37:55 GMT FROM: Aprajita Hajela at Northwestern U A. Hajela, R. Margutti (Northwestern U.), T. Laskar (U. Bath), K. D. Alexander, W. Fong (Northwestern U.), A. Kathirgamaraju (UC Berkeley), D. Giannios (Purdue U.), D. Coppejans, G. Terreran, A. Baldeschi, K. Paterson, M. Stroh, P. K. Blanchard (Northwestern U.), E. Berger, T. Eftekhari, G. Hosseinzadeh, S. Gomez, V. A. Villar (Harvard U), P. K. G. Williams (Harvard U and AAS), M. Nicholl (U. Birmingham), R. Chornock (Ohio U.), P. S. Cowperthwaite (Carnegie Observatories), A. MacFadyen (NYU), B. D. Metzger, L. Sironi (Columbia U.), D. Radice (Princeton) report: We initiated a new round of observations of the NS merger GW170817 with the Chandra X-ray Observatory (CXO) to continue following its evolution at ~ 2.5 years after the merger. Four observations will be acquired between March 9 and March 15, for a total exposure time of 100 ks. Here we report on the first observation (ObsID 21323, PI Margutti; program 20500299), which was acquired on March 09, 2020 at 22:04:48 UT (~935 days since merger) with an exposure time of 24.29 ks. X-ray emission is detected at the location of GW170817 with a significance of ~ 3-sigma (Gaussian equivalent) and a 0.5-8 keV count-rate of (1.2 +/- 0.7)e-04 c/s, and a total of ~ 2.8 net photons. Assuming a simple power-law spectrum with photon index Gamma=1.6 and no intrinsic absorption, as found in previous Chandra observations (e.g. Hajela et al. 2019, ApJL, 886L, 17H), and following the same spectra-extraction procedure as in Hajela et al. 2019, the count-rate above translates into an unabsorbed flux of ~ (3.2 +/- 1.9)e-15 erg/s/cm2 (0.3-10 keV). The Galactic neutral hydrogen column density in the direction of the transient is N_H = 7.8e+20cm-2 (Kalberla et al. 2005). This X-ray flux measurement is nominally above, yet statistically consistent with the off-axis jet model predictions given the large flux uncertainties. Further CXO observations comprising the remaining exposure time of ~75 ks are scheduled in the next few days and will help quantify the statistical evidence for the possible departure from the off-axis jet model (which might represent the onset of the kilonova afterglow). An updated plot with the most recent results can be found at this link: https://sites.google.com/u.northwestern.edu/xray-observations-of-gw170817/home We thank the entire Chandra team for making these observations possible. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 27411 SUBJECT: GW170817: Continued X-ray emission detected with Chandra at 940 days post-merger DATE: 20/03/18 17:59:10 GMT FROM: Eleonora Troja at NASA/GSFC/UMD E. Troja (UMD/NASA/GSFC), L. Piro (INAF/IAPS), G. Ryan (UMD), H. van Eerten (Bath U.), B. Zhang (UNLV) ob behalf of a larger collaboration The Chandra X-ray Observatory re-observed the field of GW170817 between March 9th and March 15th, 2020,and performed four short exposures observations (ObsIDs: 21323, 23183, 23184, 23185) for a total of 96 ks, as part of its on-going monitoring program. At the afterglow position, an X-ray source is detected with significance >4.5 sigma at an average count rate of (8+/-0.4)e-05 cts/s in the 0.5-8.0 keV energy band. By using an absorbed power-law model with absorption column fixed at the Galactic value of 7.5E20 cm^-2 and a photon index Gamma=1.585, as derived from our broadband analysis, we estimate an unabsorbed X-ray flux of (1.1 +/- 0.6)E-15 erg/cm2/s in the 0.3-10 keV energy band. The quoted error is at the 68% confidence level. This new measurement is higher than earlier predictions of a structured jet, based on a full year of data (Troja E., et al., 2019, MNRAS, 489, 1919), yet still consistent with this model within the uncertainties. Additional components of emission, such as continued energy injection from a long-lived neutron star (Piro L., et al., 2019, MNRAS, 483, 1912) or afterglow from the sub-relativistic ejecta (Kathirgamaraju A., Giannios D., Beniamini P., 2019, MNRAS, 487, 3914), cannot be excluded at this time. Further analysis is on-going. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 27414 SUBJECT: Chandra observations of GW170817 at 2.5 years since merger (All epochs 4 of 4) DATE: 20/03/19 03:15:10 GMT FROM: Aprajita Hajela at Northwestern U A. Hajela, R. Margutti (Northwestern U.), T. Laskar (U. Bath), K. D. Alexander, W. Fong (Northwestern U.), A. Kathirgamaraju (UC Berkeley), D. Giannios (Purdue U.), D. Coppejans, G. Terreran, A. Baldeschi, K. Paterson, M. Stroh, P. K. Blanchard (Northwestern U.), E. Berger, T. Eftekhari, G. Hosseinzadeh, S. Gomez, V. A. Villar (Harvard U), P. K. G. Williams (Harvard U and AAS), M. Nicholl (U. Birmingham), R. Chornock (Ohio U.), P. S. Cowperthwaite (Carnegie Observatories), A. MacFadyen (NYU), B. D. Metzger, L. Sironi (Columbia U.), D. Radice (PSU) report: We carried out Chandra X-ray observations to follow the evolution of GW170817 at t ~ 935-941 days after the neutron star merger, for a total exposure time of ~96 ks. The observations were taken in 4 distinct exposures of ~ 24ks, ~16ks, ~19ks, and ~36 ks, respectively (ObsID 21323, 23183, 23184 and 23185; PI Margutti; program 20500299, for which we waived proprietary data rights). The observations were taken on March 09, 2020 through March 15, 2020. We reported the results from our first observation (ObsID 21323) in Hajela et al. (GCN 27357). Here we report on the results from our entire data set of 96ks, using the most recent data products distributed after a data-processing issue affecting ObsID 23185 was resolved by the CXC-DS's SAP team. An earlier report can be found in Troja et al., GCN 27411. X-ray emission is detected at the location of GW170817 with a significance of ~5 sigma with a total of ~7 source photons above background in the merged file, which translates to a 0.5-8 keV count-rate of (7.2 +/- 2.7)e-5 cts/s. We perform a joint spectral analysis of all the observations using a simple power-law spectral model with photon index Gamma ~ 1.6 and NHint = 0 cm-2, as found from the homogeneous modeling of all previous Chandra observations (e.g. Hajela et al. 2019, ApJL, 886L, 17H). We freeze the galactic NH = 7.8e+20 cm-2 (Kalberla et al., 2005) and derive an unabsorbed flux of (2.3 +/- 0.9)e-15 erg/cm2/s (0.3-10 keV energy range) with 1-sigma uncertainties. The flux measurement derived here is slightly in excess to, but consistent with the predictions from updated off-axis jet models that best fitted the multi-wavelength afterglow until t~743 days. A similar conclusion was initially reported by Hajela et al., GCN 27357, and later by Troja et al., GCN 27411. An updated light-curve plot is linked here: https://sites.google.com/u.northwestern.edu/xray-observations-of-gw170817/home These observations might represent the last X-ray detection of the jet afterglow of GW170817. Future Chandra observations are planned to be acquired in December 2020 as part of our program. We thank the entire Chandra team for making these observations possible. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29019 SUBJECT: Chandra observations of GW170817 at ~3.3 years since merger (Observation 1 of 4) DATE: 20/12/09 22:38:37 GMT FROM: Aprajita Hajela at Northwestern U A. Hajela, R. Margutti, K. D. Alexander (Northwestern U.), T. Laskar (U. of Bath), D. Giannios (Purdue U.), V. A. Villar (Columbia U.) report: We observed GW170817 with the Chandra X-ray Observatory (CXO) at t =1209 days (~3.3 years) after the binary neutron star merger. Here we report the preliminary results from the analysis of the first epoch of data acquired so far, for a total exposure time of 29.7 ks (out of a total of ~100 ks to be completed over the next few days) corresponding to ObsID 22677 (PI Margutti; program 21510449). No X-ray emission is detected at the location of GW170817 and we infer a 3-sigma 0.5-8 keV count-rate upper limit of 1.0e-4 cts/s. Assuming a simple power-law spectral model with a photon index Gamma =1.57 and no intrinsic absorption NHint = 0 cm-2 (as found from previous CXO observations of GW170817, e.g., Hajela et al. 2019), the corresponding 3-sigma absorbed flux limit is Fx<1.6e-15 erg/cm2/s (0.3-10 keV), which is Lx< 3.5e+38 erg/s at the distance of 40.7 Mpc (Cantiello et al., 2018). The Galactic neutral hydrogen column density in the direction of GW170817 is NH,gal = 7.8e+20 cm-2 (Kalberla et al., 2005). As a comparison, the off-axis jet models that best fit the earlier multi-band evolution of the afterglow predict a luminosity of Lx~1.5e+38 erg/s (0.3-10 keV) at the present epoch, which is below the sensitivity of current CXO observations. Further Chandra observations planned in the next few days will probe deeper fluxes. We thank the entire Chandra team for scheduling and executing these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29038 SUBJECT: Long-lasting X-ray emission from GW170817 detected by Chandra DATE: 20/12/14 12:29:41 GMT FROM: Eleonora Troja at NASA/GSFC/UMD E. Troja (UMD/GSFC), L. Piro (INAF/IAPS), G. Ryan (UMD), B. O' Connor (UMD/GWU), H. van Eerten (U. Bath), T. Sakamoto (AGU) report: We analyzed the latest Chandra observations of GW170817 carried out between Dec 09 and Dec 13, 2020 for a total exposure of about 65 ks (out of 100 ks approved for program 21510449; PI: Margutti) At the transient position we detect a total of 9 counts within a circular region of 1 arcsec radius, corresponding to a count rate (1.5 +/- 0.5)E-04 cts/s (0.5-8.0 keV). This is slightly higher than the value measured at 940 days (0.8 +/- 0.3)E-04 cts/s (Troja et al., 2020, MNRAS, 498, 5643) and consistent within the errors. By using a power-law spectrum with photon index Gamma=1.57, we derive an X-ray flux of (2.6 +/- 0.9)E-15 erg/cm2/s. Further analysis is on-going. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29041 SUBJECT: Potential X-ray KN afterglow from Chandra observations of GW170817 ~3.3 years since merger (3 Epochs of 4) DATE: 20/12/14 17:55:09 GMT FROM: Aprajita Hajela at Northwestern U A. Hajela, R. Margutti, K. D. Alexander, W. Fong (Northwestern U.), T. Laskar (Bath), D. L. Coppejans (Northwestern U.), V. A. Villar (Columbia U.), D. Giannios (Purdue U.), T. Eftekhari (Harvard U.), L. Sironi (Columbia), B. Margalit (Berkeley) report: We observed GW170817 with the Chandra X-ray Observatory (CXO) at t ~ 1209-1212 days (~3.3 years) after the binary neutron star merger. We report here the preliminary results from the first three epochs acquired so far, for a total exposure time of ~ 64 ks (out of a total of 100 ks requested; we will report on the results from the complete data set in the next few days). The observations were taken in three distinct exposures of ~30, ~18, and ~17 ks, corresponding to ObsID 22677, 24888, and 24889, respectively (PI Margutti; program 21510449). Preliminary results on these data have been reported in Troja et al. (GCN 29038). We find evidence for statistically significant X-ray emission at the location of GW170817 in the merged file with a statistical significance of >5 sigma (Gaussian equivalent) corresponding to a net count-rate of (1.2+\- 0.4)e-04 (0.5 - 8 keV). We perform a joint spectral fit of all three epochs with a simple power-law model using a photon index Gamma ~ 1.6, no intrinsic absorption NHint = 0 cm-2 (as found in e.g. Hajela et al. 2019) and Galactic neutral hydrogen column density NH,gal = 7.8e+20 cm-2 (Kalberla et al., 2005). With these spectral parameters we derive an unabsorbed flux of 4.4 (+1.78, -1.50) e-15 erg/cm2/s (0.3-10 keV, 1-sigma uncertainties), corresponding to a luminosity of 8.7 (+3.5, -2.9)e+38 erg/s at the distance of 40.7 Mpc (Cantiello et al., 2018). These observations are consistent with a constant X-ray flux at t> 580 days, which deviates from the predictions of the off-axis jet afterglow model (e.g. Hajela et al. 2019). The derived flux at 3.3 yrs after the merger is in excess to the structured jet model that best described all the observations up to t ~ 743 days after the merger and might represent the first evidence for the emergence of the kilonova afterglow ( https://sites.google.com/u.northwestern.edu/synchrotron-emission-from-gw17/home ). We thank the entire Chandra team for scheduling and executing these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29053 SUBJECT: VLA observations of GW170817 at ~3.3 years post-merger DATE: 20/12/16 01:40:37 GMT FROM: Kate Alexander at Northwestern U K. D. Alexander, A. Hajela, R. Margutti, J. Bright (Northwestern U.), T. Eftekhari (Harvard U.), A. Kathirgamaraju (UC Berkeley), and E. Berger (Harvard U.) report on behalf of a larger collaboration: We observed GW170817 with the NSF's Karl G. Jansky Very Large Array (the VLA) at t =1216 days (~3.3 years) after the binary neutron star merger (joint program SL0449, PI: Margutti). In our preliminary analysis, no radio emission is detected at the location of GW170817; we infer a 3-sigma upper limit of ~13 microJy at a central frequency of 3 GHz. Assuming the X-ray flux density recently reported by Hajela et al. (GCN 29041) and a simple power-law spectrum, this is fully consistent with the F_nu ~ nu^-0.575 spectrum observed throughout GW170817's earlier evolution (e.g. Hajela et al. 2019). We thank the VLA staff for scheduling and executing these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29055 SUBJECT: Chandra observations of GW170817 at ~3.3 years since merger (Full report) DATE: 20/12/16 13:28:30 GMT FROM: Aprajita Hajela at Northwestern U A. Hajela, R. Margutti, K. D. Alexander, W. Fong (Northwestern U.), E. Berger (Harvard), T. Laskar (Bath), T. Eftekhari (Harvard), D. Giannios (Purdue U.), P. K. Blanchard, R. Chornock, D. L. Coppejans (Northwestern U.), V. A. Villar (Columbia U.), P. Cowperthwaite (Carnegie), L. Sironi (Columbia), B. Margalit (Berkeley) report: We report on the complete Chandra data set of observations of GW170817 acquired at t=1209-1213 days since merger (IDs 22677, 24887, 24888, and 24889; PI Margutti; program 21510449) for a total exposure time of ~91 ks. Preliminary results from a subset of these observations have been reported by Hajela et al., GCN 29041, GCN 29019; Troja et al., GCN 29038. We confirm the presence of significant X-ray emission from GW170817 (significance of detection > 5 sigma, Gaussian equivalent) from the merged observations, with a source count rate of (0.9 +/- 0.3) e-4 cps (0.5-8 keV). From a joint spectral fit with a simple power-law spectral model using a photon index Gamma ~ 1.6, no intrinsic absorption NHint = 0 cm-2 (as found in e.g. Hajela et al. 2019), and Galactic neutral hydrogen column density NH,gal = 7.8e+20 cm-2 (Kalberla et al., 2005), we estimate an unabsorbed flux of 3.46(+1.06 -1.31) e-15 erg/cm2/s (0.3-10 keV, 1-sigma uncertainties), corresponding to a luminosity of 6.9 (+2.1 -2.6) e+38 erg/s at the distance of 40.7 Mpc (Cantiello et al., 2018). The observed emission is a factor of ~2 brighter than the first X-ray non-detection of GW170817 at ~2 days after merger. As previously reported in Hajela et al., GCN 29041, the inferred flux is in excess to the extrapolation of the off-axis jet model that best fits the broad-band afterglow observations at t<580 days (e. g., Hajela et al. 2019) and might represent the emergence of a new component of emission. An updated plot of the X-ray evolution of GW170817 can be found here: https://sites.google.com/u.northwestern.edu/synchrotron-emission-from-gw17/home We thank the entire Chandra team for scheduling and executing these observations. We thank the entire Chandra team for scheduling and executing these observations. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29263 SUBJECT: GW170817: HST observations at 3.4 years from merger DATE: 21/01/05 19:06:43 GMT FROM: Charles Kilpatrick at UC Santa Cruz C. D. Kilpatrick, W. Fong, A. Hajela, K. D. Alexander (Northwestern), E. Berger (Harvard), P. K. Blanchard, R. Chornock, R. Margutti, K. Paterson, J. Rastinejad (Northwestern) report: We report on new Hubble Space Telescope (HST) observations of the near-infrared counterpart to GW170817 at a mid-time of 4.98 Jan 2021 UT, 1236.45 days from merger (GO-15886, PI Fong). These observations consist of 3 orbits observed in WFC3/IR F140W for a total of 7.8 ks on-source exposure time. Compared to previous F606W HST imaging of the optical and near-infrared afterglow to GW170817 (Lyman et al. 2018, Nature Astronomy, 2, 751; Lamb et al. 2019, ApJL, 870, L15; Fong et al. 2019, ApJL, 883, L1), we do not visually detect a counterpart at the site of GW170817 in the latest observations. We injected artificial sources at the afterglow site and recover a 3-sigma limiting magnitude of >26.3 mag (AB and without correcting for Galactic extinction). Based on recent Chandra detections of the X-ray counterpart to GW170817 at 1209-1213 days after merger (Hajela et al., GCN 29041, GCN 29019; Troja et al., GCN 29038) as well as radio non-detections with the VLA at 1216 days post-merger (Alexander et al., GCN 29053), we consider whether this limit is constraining in the context of the detection discussed in Hajela et al., GCN 29055. Assuming the counterpart had an unabsorbed flux of 3.46e-15 erg/cm2/s (0.3-10 keV) at that time and a Gamma~1.6 photon index, we infer that the source would have f_F140W = 1.5e-8 Jy or m_F140W = 28.5 mag (AB; unabsorbed) or 28.6 mag (AB; accounting for Galactic extinction) in the latest observations. Similarly, the radio observations yielded a 3-sigma limiting flux of 13 muJy at a central frequency of 3 GHz, which imply that m_F140W > 28 mag for the same photon index, significantly fainter than our limit. Thus the latest observations are not constraining for this model. However, additional HST observations are planned in F814W, F110W, and F160W between now and 2021 March 1 with comparable exposure times in each filter, enabling deeper constraints on the optical and near-infrared counterpart to GW170817 over a broader range of its spectral energy distribution. We thank the STScI staff for facilitating these observations, especially our program coordinator Shelly Meyett. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 29375 SUBJECT: Continued Chandra observations of GW170817 at ~3.3 years since merger DATE: 21/01/30 18:21:47 GMT FROM: Aprajita Hajela at Northwestern U A. Hajela, R. Margutti, J. Bright, K. D. Alexander, W. Fong (Northwestern U.), E. Berger (Harvard), R. Chornock, D. L. Coppejans, P. Blanchard (Northwestern U.), V. A. Villar (Columbia U.), T. Eftekhari (Harvard U), A. Kathirgamaraju (UC Berkeley), D. Giannios (Purdue U.), T. Laskar (Bath), J. Zrake (Clemson), A. MacFadyen (NYU), K. Paterson (Northwestern U.) report: We acquired 3 distinct exposures (ObsID 23870, 24923, and 24924) of GW170817 with the Chandra X-ray Observatory (CXO) between January 18 and January 27, 2021, under our program 22510329 (PI Margutti), for a total exposure time of ~98 ks. We initiated these observations after we inferred a potential excess of X-ray emission compared to our off-axis jet model in our previous round of observations (ObsID 22677, 24887, 24888, and 24889; results reported in Hajela et al., GCN 29055; also see Troja et al. GCN 27411). The 3 new observations combined with our previous round span 1209-1258 days post-merger and have a mean epoch of 1234 days. We merge all 7 observations and find significant X-ray emission at the location of GW170817 at the level of ~5 sigma (Gaussian equivalent). From a joint spectral fit with a simple power-law spectral model using a photon index Gamma ~ 1.6, no intrinsic absorption NHint = 0 cm-2 (as found in e.g. Hajela et al. 2019), and Galactic neutral hydrogen column density NH,gal = 7.8e+20 cm-2 (Kalberla et al., 2005), we estimate an unabsorbed flux of 2.4(+0.53 -0.82) e-15 erg/cm2/s (0.3-10 keV, 1-sigma uncertainties), corresponding to a luminosity of 4.8 (+1.1 -1.6) e+38 erg/s at the distance of 40.7 Mpc (Cantiello et al., 2018). Based on the expectations from the best-fitting off-axis jet model from Hajela+2019, the chance probability to obtain at ~1234 days after the merger an X-ray count-rate at least as large as the measured count-rate is P=0.0014 (corresponding to 3.2 sigma, Gaussian equivalent). Radio observations to date have not shown the same excess (Alexander et al. GCN 29053), but more detailed analysis is in progress. We thank the entire Chandra team for scheduling and executing these observations.