//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22790 SUBJECT: GRB 180618A: Swift detection of a burst with an optical counterpart DATE: 18/06/18 00:53:53 GMT FROM: David Palmer at LANL S. J. LaPorte (PSU), S. D. Barthelmy (GSFC), J. A. Kennea (PSU), A. Y. Lien (GSFC/UMBC), F. E. Marshall (NASA/GSFC), D. M. Palmer (LANL), M. H. Siegel (PSU) and A. Tohuvavohu (PSU) report on behalf of the Neil Gehrels Swift Observatory Team: At 00:43:13 UT, the Swift Burst Alert Telescope (BAT) triggered and located GRB 180618A (trigger=842475). Swift slewed immediately to the burst. The BAT on-board calculated location is RA, Dec 169.937, +73.848 which is RA(J2000) = 11h 19m 45s Dec(J2000) = +73d 50' 52" with an uncertainty of 3 arcmin (radius, 90% containment, including systematic uncertainty). The BAT light curve showed a single FRED structure with a duration of about 20 sec. The peak count rate was ~10000 counts/sec (15-350 keV), at ~0 sec after the trigger. The XRT began observing the field at 00:44:30.5 UT, 77.6 seconds after the BAT trigger. XRT found a bright, uncatalogued X-ray source located at RA, Dec 169.9415, 73.8358 which is equivalent to: RA(J2000) = +11h 19m 45.96s Dec(J2000) = +73d 50' 08.9" with an uncertainty of 5.4 arcseconds (radius, 90% containment). This location is 44 arcseconds from the BAT onboard position, within the BAT error circle. No event data are yet available to determine the column density using X-ray spectroscopy. The initial flux in the 2.5 s image was 1.27e-09 erg cm^-2 s^-1 (0.2-10 keV). UVOT took a finding chart exposure of 150 seconds with the White filter starting 86 seconds after the BAT trigger. There is a candidate afterglow in the list of sources generated on-board at RA(J2000) = 11:19:45.78 = 169.94074 DEC(J2000) = +73:50:13.3 = 73.83704 with a 90%-confidence error radius of about 1.10 arc sec. This position is 4.5 arc sec. from the center of the XRT error circle. The estimated magnitude is 17.81. No correction has been made for the expected extinction corresponding to E(B-V) of 0.07. Burst Advocate for this burst is S. J. LaPorte (extragsam AT gmail.com). Please contact the BA by email if you require additional information regarding Swift followup of this burst. In extremely urgent cases, after trying the Burst Advocate, you can contact the Swift PI by phone (see Swift TOO web site for information: http://www.swift.psu.edu/too.html.) //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22791 SUBJECT: GRB 180618A: Enhanced Swift-XRT position DATE: 18/06/18 03:26:07 GMT FROM: Phil Evans at U of Leicester M.R. Goad, J.P. Osborne, A.P. Beardmore and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team. Using 1241 s of XRT Photon Counting mode data and 1 UVOT images for GRB 180618A, we find an astrometrically corrected X-ray position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 169.94141, +73.83731 which is equivalent to: RA (J2000): 11h 19m 45.94s Dec (J2000): +73d 50' 14.3" with an uncertainty of 1.7 arcsec (radius, 90% confidence). This position may be improved as more data are received. The latest position can be viewed at http://www.swift.ac.uk/xrt_positions. Position enhancement is described by Goad et al. (2007, A&A, 476, 1401) and Evans et al. (2009, MNRAS, 397, 1177). This circular was automatically generated, and is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22792 SUBJECT: GRB 180618A: LT prompt observations DATE: 18/06/18 08:18:45 GMT FROM: Cristiano Guidorzi at Ferrara U,Italy C. Guidorzi (U. Ferrara), S. Kobayashi (LJMU), C.G. Mundell (U. Bath), A. Gomboc (U. Nova Gorica), I.A. Steele (LJMU) on behalf of a large collaboration report: The 2-m Liverpool Telescope automatically began observing Swift GRB 180618A (LaPorte et al. GCN 22790) on June 18, 00:46:30 UT (197 s since the GRB trigger time) with the RINGO3 polarimeter and the IO:O camera in the SDSS-R filter. The optical counterpart identified by Swift-UVOT is clearly detected with r'=19.36 +- 0.05 mag in a 6x10s exposure at a mid time of 36.3 minutes post GRB, as calibrated against nearby SDSS objects. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22793 SUBJECT: GRB 180618A: Swift-XRT refined Analysis DATE: 18/06/18 10:23:59 GMT FROM: Phil Evans at U of Leicester V. D'Elia (ASDC), A. D'Ai (INAF-IASFPA), A. Melandri (INAF-OAB), D.N. Burrows (PSU), A. Tohuvavohu (PSU), S. J. LaPorte (PSU), P.A. Evans (U. Leicester), S.L. Gibson (U. Leicester), Z. Liu (NAOC / U. Leicester) and S.J. LaPorte report on behalf of the Swift-XRT team: We have analysed 7.8 ks of XRT data for GRB 180618A (LaPorte et al. GCN Circ. 22790), from 83 s to 24.6 ks after the BAT trigger. The data comprise 293 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Goad et al. (GCN Circ. 22791). The light curve can be modelled with an initial power-law decay with an index of alpha=0.66 (+0.19, -0.31), followed by a break at T+158 s to an alpha of 1.80 (+/-0.05). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.91 (+/-0.09). The best-fitting absorption column is 2.0 (+0.4, -0.3) x 10^21 cm^-2, in excess of the Galactic value of 4.4 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 2.23 (+0.22, -0.21) and a best-fitting absorption column of 2.9 (+0.8, -0.7) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.3 x 10^-11 (5.4 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 2.9 (+0.8, -0.7) x 10^21 cm^-2 Galactic foreground: 4.4 x 10^20 cm^-2 Excess significance: 5.3 sigma Photon index: 2.23 (+0.22, -0.21) If the light curve continues to decay with a power-law decay index of 1.80, the count rate at T+24 hours will be 1.9 x 10^-4 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 6.4 x 10^-15 (1.1 x 10^-14) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00842475. This circular is an official product of the Swift-XRT team. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22794 SUBJECT: GRB 180618A: Fermi GBM detection DATE: 18/06/18 15:47:53 GMT FROM: Rachel Hamburg at UAH R. Hamburg (UAH) and E. Bissaldi (Politecnico & INFN Bari) report on behalf of the Fermi GBM Team: "At 00:43:13.11 UT on 18 June 2018, the Fermi Gamma-Ray Burst Monitor triggered and located GRB 180618A (trigger 550975398 / 180618030), which was also detected by the Swift/BAT (LaPorte et al. 2018, GCN 22790). The GBM on-ground location is consistent with the Swift position. The angle from the Fermi LAT boresight at the GBM trigger time is 103 degrees. The GBM light curve shows one main peak with a duration (T90) of about 3.7 s (50-300 keV). LaPorte et al. 2018 report a longer duration of ~20 s in the Swift/BAT. Given the soft tail following the initial hard spike, we suggest the discrepancy may be due to extended emission of this short GRB. The time-averaged spectrum from T0 to T0+1.8 s is adequately fit a power law function with an exponential high-energy cutoff. The power law index is 1.08 +/- 0.06 and the cutoff energy, parameterized as Epeak, is 2.8 +/- 0.8 MeV. The event fluence (10-1000 keV) in this time interval is (2.12 +/- 0.12)E-06 erg/cm^2. The 64-ms peak photon flux measured starting from T0 in the 10-1000 keV band is 14.6 +/- 1.9 ph/s/cm^2. The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog." //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22796 SUBJECT: GRB 180618A: Swift-BAT refined analysis (a short GRB with extended emission) DATE: 18/06/18 18:27:23 GMT FROM: Amy Lien at GSFC T. Sakamoto (AGU), S. D. Barthelmy (GSFC), J. R. Cummings (CPI), H. A. Krimm (NSF/USRA), S. J. LaPorte (PSU), A. Y. Lien (GSFC/UMBC), C. B. Markwardt (GSFC), J. P. Norris (BSU), D. M. Palmer (LANL), M. Stamatikos (OSU), T. N. Ukwatta (LANL) (i.e. the Swift-BAT team): Using the data set from T-239 to T+963 sec from the recent telemetry downlink, we report further analysis of BAT GRB 180618A (trigger #842475) (LaPorte et al., GCN Circ. 22790). The BAT ground-calculated position is RA, Dec = 169.948, 73.825 deg which is RA(J2000) = 11h 19m 47.6s Dec(J2000) = +73d 49' 29.3" with an uncertainty of 1.5 arcmin, (radius, sys+stat, 90% containment). The partial coding was 70%. The mask-weighted light curve shows a short multi-peaked structure from ~ T0 to ~T+0.3, followed by some extended emission that lasts till ~T+50 s. T90 (15-350 keV) is 47.4 +- 11.1 sec (estimated error including systematics). The time-averaged spectrum from T-0.06 to T+56.33 sec is best fit by a simple power-law model. The power law index of the time-averaged spectrum is 1.39 +- 0.27. The fluence in the 15-150 keV band is 6.7 +- 1.0 x 10^-7 erg/cm2. The 1-sec peak photon flux measured from T-0.08 sec in the 15-150 keV band is 2.2 +- 0.2 ph/cm2/sec. All the quoted errors are at the 90% confidence level. The structure of the burst shows similarity to those of short GRBs with extended emission, as mentioned in Hamburg et al., GCN Circ. 22794. We thus perform further analysis on the short spike and the extended emission. The spectrum of the short multi-peaked structure from T-0.056 to T+0.264 sec is best fit by a simple power-law model, with power-law index of 0.60 +- 0.24 and fluence (15-150 keV) of 1.3 +- 0.2 x 10^-7 erg/cm2. The spectrum of the extended emission from T+0.264 to T+56.328 sec is best fit by a simple power-law model, with power-law index of 1.53 +- 0.31 and fluence (15-150 keV) of 5.5 +- 1.0 x 10^-7 erg/cm2. These values are consistent with those of short GRBs with extended emission (Lien & Sakamoto et al. 2016). Using a 4-ms binned light curve, the lag analysis of the first two tallest pulses (from ~T0 to ~T+0.1 s) finds a lag of 0.7 +/- 0.9 ms for the 100-350 keV to 25-50 keV band, and 1.5 (+1.8, -1.2) ms for the 50-100 keV to 15-25 keV band. Therefore, the lag values of these short pulses are consistent with those of short GRBs. The results of the batgrbproduct analysis are available at http://gcn.gsfc.nasa.gov/notices_s/842475/BA/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22797 SUBJECT: GRB 180618A: MASTER OT observation (a short GRB with extended emission) DATE: 18/06/19 12:00:58 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs N.Tyurina, V. Lipunov, E. Gorbovskoy, V.Kornilov, A.Kuznetsov, I. Gorbunov, D. Vlasenko, D.Zimnukhov, D.Kuvshinov, P.Balanutsa, V.Vladimirov Lomonosov Moscow State University, Sternberg Astronomical Institute, Moscow State University R. Rebolo, M. Serra, N. Lodieu, G. Israelian, L. Suarez-Andres The Instituto de Astrofisica de Canarias A. Tlatov, V.Senik, D. Dormidontov Kislovodsk Solar Station of the Pulkovo Observatory R. Podesta, F. Podesta, C. Lopez, C.Francile Observatorio Astronomico Felix Aguilar (OAFA) H.Levato, C. Saffe Instituto de Ciencias Astronomicas, de la Tierra y del Espacio (ICATE) D. Buckley South African Astronomical Observatory O. Gres, N.M.Budnev , Yu.Ishmuhametova Irkutsk State University A. Gabovich, V. Yurkov, Yu. Sergienko Blagoveschensk Educational State University, Blagoveschensk MASTER-Kislovodsk robotic telescope (MASTER-Net: http://observ.pereplet.ru Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) , located in Kislovodsk Solar Station of Pulkovo observatory, was pointed to the Swift GRB180618A (LaPorte et al. GCN #22790; Sakamoto et al., GCN #22796) 25 sec after notice time and 41 sec after trigger time at 2018-06-18 00:43:53 UT. On our first (10s exposure) polarization set we haven`t found optical transient within SWIFT error-box (ra=169.933 dec=73.8478 r=0.05). The 5-sigma upper limit has been about 15.2 mag The observations made on zenit distance = 61 degrees, galaxy latitude b = 42 degree. The moon (24 % bright part) below the horizon (The altitude of the Moon is -31 degree ). Observations started at twilight and bad transparency. The sun altitude is -6.8 degree. MASTER II robotic telescope (MASTER-Net: http://observ.pereplet.ru) located in IAC was pointed to the GRB180618A 1734 sec after trigger time at 2018-06-18 01:12:07 UT. On our first (180s exposure) set we found ~19 mag optical transient within SWIFT UVOT error-box (LaPorte et al. GCN #22790; Guidorzi et al., GCN #22792;). The 5-sigma upper limit has been about 19.0 mag on single (180 s) and 20.5 on coadd (1800 s) exposures. ==================================================================== The observations made on zenit distance = 64 degrees, galaxy latitude b = 42 degree. The moon (24 % bright part) below the horizon (The altitude of the Moon is -15 degree ). The sun altitude is -38.3 degree. The object can be observed till sunrise at 2018-06-18 06:08:21 The message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22804 SUBJECT: GRB 180618A: Xinglong-2.16m optical upper limit DATE: 18/06/20 13:02:02 GMT FROM: Dong Xu at NAOC/CAS Z.P. Zhu, D. Xu, J.B. Zhang (NAOC), X. Zhang, J.H. Liu (XAO), Z.B. Dai (YNAO) report: We observed the field of GRB 180618A (LaPorte et al., GCN 22790) using the 2.16-m telescope located at Xinglong, Hebei, China, equipped with the BFOSC camera. We obtained 6x600s R-band frames, starting at 12:43:22 UT on 2018-06-19, i.e., 1.50 days after the BAT trigger. The previously detected optical afterglow of the GRB (e.g., LaPorte et al., GCN 22790; Guidorzi et al., GCN 22792; Tyurina et al., GCN 22797) was not present in our stacked image, down to a limiting magnitude of R~21.4 mag, calibrated with the SDSS field. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22809 SUBJECT: GRB 180618A: TSHAO optical upper limit DATE: 18/06/20 17:57:39 GMT FROM: Alexei Pozanenko at IKI, Moscow E. Mazaeva (IKI), A. Kusakin (FAPHI), A. Pozanenko (IKI), I. Reva (FAPHI), A. Volnova (IKI), M. Krugov (FAPHI) report on behalf of larger GRB follow-up collaboration: We observed the field of GRB GRB 180618A (LaPorte et al., GCN 22790) with Zeiss-1000 1-m telescope of Tien Shan Astronomical Observatory starting on June 18 (UT) 15:39:19. We obtained several images in R-filter. The optical afterglow (LaPorte et al., GCN 22790; Guidorzi et al., GCN 22792; Tyurina et al., GCN 22797) is not detected in a stacked image. Preliminary photometry of the field is following. Date UT start t-T0 Filter Exp. OT Err. UL (mid, days) (s) 2018-06-18 15:39:19 0.65209 R 36*120 n/d n/d 22.2 The photometry is based on several nearby SDSS-DR10 stars. Ref.stars SDSS_id R(Lupton) J112037.79+735136.8 17.37 J111905.28+734733.2 17.54 J111907.19+734657.8 17.04 //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22810 SUBJECT: GRB 180618A: Swift/UVOT Detection DATE: 18/06/20 18:15:17 GMT FROM: Mike Siegel at PSU/Swift MOC M. H. Siegel (PSU) and S. J. LaPorte (PSU) report on behalf of the Swift/UVOT team: The Swift/UVOT began settled observations of the field of GRB 180618A 86 s after the BAT trigger (LaPorte et al., GCN Circ. 22790). We confirm the previously reported fading optical afterglow, also detected by LT (Guidorzi et al., GCN Circ. 22792) and MASTER (Tyurina et al., GCN Circ. 22797). We find that the source had faded away completely by the second orbit. The detection of the afterglow in six of UVOT's filters places an upper limit on the redshift of z < 1.2. The preliminary UVOT position is: RA (J2000) = 11:19:45.84 = 169.94102 (deg.) Dec (J2000) = +73:50:13.5 = 73.83707 (deg.) with an estimated uncertainty of 0.43 arc sec. (radius, 90% confidence). Preliminary detections and 3-sigma upper limits using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) for the early exposures are: Filter T_start(s) T_stop(s) Exp(s) Mag white (fc) 86 236 147 17.46 +/- 0.04 white 86 1544 390 17.95 +/- 0.03 white 5680 7315 393 >21.09 v 628 1596 117 18.71 +/- 0.22 v 6090 6290 196 >19.25 b 553 1175 58 18.84 +/- 0.16 b 5475 7110 393 >20.39 u (fc) 298 548 246 17.50 +/- 0.06 u 298 1497 313 17.62 +/- 0.06 u 5270 6905 393 >19.94 w1 676 1472 97 18.59 +/- 0.24 w1 5065 6700 393 >19.63 m2 1254 1621 58 >17.6 w2 604 1398 97 18.85 +/- 0.28 The magnitudes in the table are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.07 in the direction of the burst (Schlegel et al. 1998). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22822 SUBJECT: Konus-Wind observation of GRB 180618A (a short GRB with extended emission) DATE: 18/06/22 10:32:51 GMT FROM: Dmitry Svinkin at Ioffe Institute D. Svinkin, S. Golenetskii, R. Aptekar, D. Frederiks, M. Ulanov, A. Tsvetkova, A. Lysenko, A. Kozlova, and T. Cline on behalf of the Konus-Wind team, report: The bright, short-duration, hard GRB 180618A (Swift-BAT detection: LaPorte et al., GCN Circ 22790; Fermi-GBM detection: Hamburg et al., GCN Circ 22794) triggered Konus-Wind at T0=2591.201 s UT (00:43:11.201). The burst light curve shows a bright multi-peaked initial pulse with a total duration of ~0.250 s, followed by an extended emission seen up to ~T0+10 s. The emission of the initial pulse is seen up to ~10 MeV. The Konus-Wind light curve of this GRB is available at http://www.ioffe.ru/LEA/GRBs/GRB180618_T02591/ As observed by Konus-Wind, the burst had a fluence of 6.24(-1.13,+1.20)x10^-6 erg/cm2, and a 16-ms peak flux, measured from T0-0.010 s, of 5.60(-1.83,+1.88)x10^-5 erg/cm2/s (both in the 20 keV - 10 MeV energy range). The time-averaged spectrum of the initial pulse (measured from T0 to T0+0.192 s) is best fit in the 20 keV - 10 MeV range by a power law with exponential cutoff model: dN/dE ~ (E^alpha)*exp(-E*(2+alpha)/Ep) with alpha = -0.36(-0.24,+0.30) and Ep = 2461(-565,+788) keV (chi2 = 47/38 dof). Fitting by a GRB (Band) model yields the same alpha and Ep, and an upper limit on the high energy photon index: beta < -2.4 (chi2 = 47/37 dof). The time-averaged spectrum of the extended emission (measured from T0+0.256 to T0+8.448 s) is best fit in the 20 keV - 2 MeV range by the CPL model with alpha = -0.68(-0.79,+1.59), Ep = 170(-66,+203) keV (chi2 = 102/98 dof). Among ~300 bursts from the Konus catalog of short GRBs (Svinkin et al., 2016, ApJS 224, 10), GRB 180618A is within top 1% in the terms of 16-ms peak energy flux and within top 15% in the terms of the total energy fluence, both in the 20 keV - 10 MeV range. In the terms of Epeak, the burst is within 1% hardest GRBs in the sample. All the quoted errors are at the 90% confidence level. All the quoted values are preliminary. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 22842 SUBJECT: GRB 180618A: AstroSat CZTI detection DATE: 18/06/25 13:49:11 GMT FROM: Vidushi Sharma at IUCAA V. Sharma and D. Bhattacharya (IUCAA), V. Bhalerao (IIT-B), A. R. Rao (TIFR) and S. Vadawale (PRL) report on behalf of the Astrosat CZTI collaboration: Analysis of Astrosat CZTI data showed the detection of a short GRB 180618A, which was also detected by Swift (LaPorte S. J. et al., GCN 22790), Fermi-GBM (Hamburg R. et al., GCN 22794), Konus-Wind (Svinkin D. et al., GCN 22822). The source was clearly detected in the 40-200 keV energy range. The light curve shows a single peak of emission with peak at 00:43:13.5 UT. The measured peak count rate is 217.1 cts/s above the background in combined data of four quadrants, with a total of 140.9 cts. The local mean background count rate was 456.9 cts/s. Using cumulative rates, we measure a T90 of 2.1 s. It was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. CZTI GRB detections are reported regularly on the payload site at http://astrosat.iucaa.in/czti/?q=grb. 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.