//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25183 SUBJECT: LIGO/Virgo S190728q Global MASTER-Net observations report DATE: 19/07/28 07:17:09 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs V. Lipunov, E. Gorbovskoy, V.Kornilov, N.Tyurina, P.Balanutsa, A.Kuznetsov, F.Balakin, V.Vladimirov, D. Vlasenko, I.Gorbunov, D.Zimnukhov, V.Senik, T.Pogrosheva, D.Kuvshinov (Lomonosov Moscow State University, SAI, Physics Department), R. Podesta, C.Lopez, F. Podesta, C.Francile (Observatorio Astronomico Felix Aguilar OAFA), H.Levato (Instituto de Ciencias Astronomicas, de la Tierra y del Espacio ICATE), R. Rebolo, M. Serra (The Instituto de Astrofisica de Canarias) D. Buckley (South African Astronomical Observatory), O.A. Gres, N.M. Budnev, O.Ershova (Irkutsk State University, API), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), V. Yurkov, A. Gabovich, Yu. Sergienko (Blagoveschensk Educational State University) MASTER-OAFA robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Argentina (OAFA observatory of San Juan National University) started inspect of the LIGO/Virgo S190728q errorbox 16 sec after notice time and 919 sec after trigger time at 2019-07-28 07:00:29 UT, with upper limit up to 18.1 mag. The observations began at zenit distance = 57 deg. The sun altitude is -56.5 deg. The galactic latitude b = -60 deg., longitude l = 98 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/ligo_1.php?id=10605 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 1010 | 2019-07-28 07:00:29 | MASTER-OAFA | ( 21h 34m 34.53s , +22d 52m 58.40s) | C | 180 | 18.1 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25185 SUBJECT: LIGO/Virgo S190728q: Upper limits from IceCube neutrino searches DATE: 19/07/28 07:27:06 GMT FROM: Raamis Hussain at IceCube IceCube Collaboration (http://icecube.wisc.edu/) reports: Searches [1,2] for track-like muon neutrino events detected by IceCube consistent with the sky localization of gravitational-wave candidate S190728q in a time range of 1000 seconds [3] centered on the alert event time (2019-07-28 06:36:50.547 UTC to 2019-07-28 06:53:30.547 UTC) have been performed. During this time period IceCube was collecting good quality data. No significant track-like events are found in spatial coincidence of S190728q calculated from the map circulated in the 2-Preliminary notice. IceCube's sensitivity assuming an E^-2 spectrum (E^2 dN/dE) to neutrino point sources within the locations spanned by the 90% spatial containment of S190728q ranges from 0.029 to 1.150 GeV cm^-2 in a 1000 second time window. The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc@icecube.wisc.edu [1] Bartos et al. arXiv:1810.11467 (2018) and Countryman et al.arXiv:1901.05486 (2019) [2] Braun et al., Astroparticle Physics 29, 299 (2008) [3] Baret et al., Astroparticle Physics 35, 1 (2011) //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25187 SUBJECT: LIGO/Virgo S190728q: Identification of a GW compact binary merger candidate DATE: 19/07/28 08:47:18 GMT FROM: Sarah Antier at APC The LIGO Scientific Collaboration and the Virgo Collaboration report: We identified the compact binary merger candidate S190728q during real-time processing of data from LIGO Hanford Observatory (H1), LIGO Livingston Observatory (L1), and Virgo Observatory (V1) at 2019-07-28 06:45:10.529 UTC (GPS time: 1248331528.529). The candidate was found by the GstLAL [1], CWB [2], MBTAOnline [3], and SPIIR [4] analysis pipelines. S190728q is an event of interest because its false alarm rate, as estimated by the online analysis, is 2.5e-23 Hz, or about one in 1e15 years. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S190728q The classification of the GW signal, in order of descending probability, is MassGap (52%), BBH (34%), NSBH (14%), Terrestrial (<1%), or BNS (<1%). Assuming the candidate is astrophysical in origin, there is strong evidence against the lighter compact object having a mass < 3 solar masses (HasNS: <1%). Using the masses and spins inferred from the signal, there is strong evidence against matter outside the final compact object (HasRemnant: <1%). One sky map is available at this time and can be retrieved from the GraceDB event page:  * bayestar.fits.gz, an updated localization generated by BAYESTAR [5], distributed via GCN notice about 55 minutes after the candidate For the bayestar.fits.gz sky map, the 90% credible region is 543 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 795 +/- 197 Mpc (a posteriori mean +/- standard deviation). Note that both skymap and source-classification were updated for the event in favor of a triple detector event. For further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo Public Alerts User Guide .  [1] Messick et al. PRD 95, 042001 (2017)  [2] Klimenko et al. PRD 93, 042004 (2016)  [3] Adams et al. CQG 33, 175012 (2016)  [4] Qi Chu, PhD Thesis, The University of Western Australia (2017)  [5] Singer & Price PRD 93, 024013 (2016) //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25188 SUBJECT: LIGO/Virgo S190728q: Coverage and upper limits from MAXI/GSC observations DATE: 19/07/28 09:03:06 GMT FROM: Motoko Serino at RIKEN/MAXI H. Negoro (Nihon U.), N. Kawai, M. Sugizaki (Tokyo Tech), S. Sugita, M. Serino (AGU), M. Nakajima, W. Maruyama, M. Aoki, K. Kobayashi (Nihon U.), T. Mihara, T. Tamagawa, M. Matsuoka (RIKEN), T. Sakamoto, H. Nishida, A. Yoshida (AGU), Y. Tsuboi, W. Iwakiri, R. Sasaki, H. Kawai, T. Sato (Chuo U.), M. Shidatsu (Ehime U.), M. Oeda, K. Shiraishi (Tokyo Tech), S. Nakahira, Y. Sugawara, S. Ueno, H. Tomida, M. Ishikawa, N. Isobe, R. Shimomukai, M. Tominaga (JAXA), Y. Ueda, A. Tanimoto, S. Yamada, S. Ogawa, K. Setoguchi, T. Yoshitake (Kyoto U.), H. Tsunemi, T. Yoneyama, K. Asakura, S. Ide (Osaka U.), M. Yamauchi, S. Iwahori, Y. Kurihara, K. Kurogi, K. Miike (Miyazaki U.), T. Kawamuro (NAOJ), K. Yamaoka (Nagoya U.), Y. Kawakubo (LSU) report on behalf of the MAXI team: We examined MAXI/GSC all-sky X-ray images (2-20 keV) after the LVC trigger S190728q at 2019-07-28 06:45:10.529 UTC (GCN 25187). At the trigger time of S190728q, the high-voltage of MAXI/GSC was on, but the FOV was out of the 90% credible region of the bayestar skymap. The first one-orbit (92 min) scan observation with GSC after the event covered 61% of the 90% credible region of the bayestar skymap from 07:13:51 to 07:17:46 UTC (T0+1721 to T0+1956 sec). No significant new source was found in the region in the one-orbit scan observation. A typical 1-sigma averaged upper limit obtained in one scan observation is 20 mCrab at 2-20 keV. If you require information about X-ray flux by MAXI/GSC at specific coordinates, please contact the submitter of this circular by email. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25189 SUBJECT: LIGO/Virgo S190728q: SPI-ACS/INTEGRAL data analysis DATE: 19/07/28 09:26:53 GMT FROM: Alexei Pozanenko at IKI, Moscow P. Minaev (IKI), A. Pozanenko (IKI), I. Chelovekov (IKI), S. Grebenev (IKI) on behalf of IKI GRB FuN collaboration report: Using SPI-ACS/INTEGRAL public data we performed a search for counterpart of S190728q (LVC, GCN 25187). We found significant excesses at +/- 100 sec around event time T0=2019-07-28T06:45:10.567644: time after T0, duration, significance, fluence, assumed Eiso -11.5, 1 s, 4.2 sigma, (1.7 +/- 0.4)*10e-7 erg/sm, (1.1 +/-0.3)*10e49 erg 42.5 s, 1 s, 3.5 sigma, (1.4 +/- 0.4)*10e-7 erg/sm2, (0.88+/-0.26)*10e49 erg The fluence of the excesses is calculated for the angle of 74 degrees toward most probable area of localization (LVC, GCN 25187). Eiso is calculated assuming luminosity distance of 795 Mpc (LVC, GCN 25187). The light curve of SPI-ACS can be found at http://grb.rssi.ru/S190728q/S190728q_SPI-ACS_1sec_LC.png //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25190 SUBJECT: LIGO/Virgo S190728q: No counterpart candidates in INTEGRAL SPI-ACS prompt observation DATE: 19/07/28 09:33:07 GMT FROM: Maeve Doyle at U College Dublin, Ireland Maeve Doyle (UCD, Ireland), Alexander Lutovinov (IKI, Moscow) V. Savchenko, C. Ferrigno (ISDC/UniGE, Switzerland) J. Rodi (IAPS-Roma, Italy) A. Coleiro (APC, France) S. Mereghetti (INAF IASF-Milano, Italy) on behalf of the INTEGRAL multi-messenger collaboration: https://www.astro.unige.ch/cdci/integral-multimessenger-collaboration Using INTEGRAL/SPI-ACS realtime data (following [1]) we have performed a search for a prompt gamma-ray counterpart of S190728q (GCN 25187). At the time of the event (2019-07-28 06:45:10 UTC, hereafter T0), INTEGRAL was operating in nominal mode. The peak of the event localization probability was at an angle of 91 deg with respect to the spacecraft pointing axis. This orientation implies strongly suppressed (5.3% of optimal) response of ISGRI, strongly suppressed (13% of optimal) response of IBIS/Veto, and somewhat suppressed (58% of optimal) response of SPI-ACS. The background within +/-300 seconds around the event was rather stable (excess variance 1.2). We have performed a search for any impulsive events in INTEGRAL SPI- ACS (as described in [2]) data. We detect a marginal event (S/N 5.22, local FAP 3.27 equivalent sigma) at 0.05s time scale at T0+201.01. Peak count rate of the signal in SPI-ACS is 9629 cts/s, which corresponds to 2.03e-06 to 2.39e-06 erg/cm2/s depending on the location within the 50% LIGO/Virgo Event localization region and assuming a typical short GRB spectrum. This estimate does not explore uncertainty related to the unknown event spectrum, systematic uncertainty on the response of 20%, or any dead-time correction. For the mean distance to the source of 795.0 Mpc this corresponds to the isotropic-equivalent luminosity between 1.53e+50 to 1.8e+50 erg/s. We derive a preliminary estimate of the associated FAP higher than 0.5 (less than 0.67 sigma). This tentatively indicates a random coincidence. Further analysis, taking into account accurate FAR measured on the basis of the study of the background during days surrounding the event will be reported in forthcoming circulars. Otherwise, we estimate a 3-sigma upper limit on the 75-2000 keV fluence of 2.6e-07 erg/cm^2 (within the 50% probability containment region of the source localization) for a burst lasting less than 1 s with a characteristic short GRB spectrum (an exponentially cut off power law with alpha=-0.5 and Ep=600 keV) occurring at any time in the interval within 300 s around T0. For a typical long GRB spectrum (Band function with alpha=-1, beta=-2.5, and Ep=300 keV), the derived peak flux upper limit is ~2.1e-07 (7.9e-08) erg/cm^2/s at 1 s (8 s) time scale in 75-2000 keV energy range. In this case, For the mean reported distance 795.0 Mpc this corresponds to the limit on the total isotropic equivalent energy in 1 s of 1.9e+49 erg for the short GRB spectrum and for a long GRB spectrum the isotropic equivalent luminosity can be estimated in 1 s (8 s) as 1.6e+49 erg/s (6e+48 erg/s). All results quoted are preliminary. This circular is an official product of the INTEGRAL Multi-Messenger team. [1] Savchenko et al. 2017, A&A 603, A46 [2] Savchenko et al. 2012, A&A 541A, 122S //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25191 SUBJECT: LIGO/Virgo S190728q: No counterpart candidates in HAWC observations DATE: 19/07/28 09:55:25 GMT FROM: Edna L. Ruiz-Velasco at MPIK The HAWC Collaboration (https://www.hawc-observatory.org) reports: The HAWC Collaboration performed a follow-up of the gravitational wave trigger S190728q (GCN 25187). At the time of the trigger the HAWC local zenith was oriented towards (RA, Dec) = (309.4 deg, 18.9 deg). 73% of the GW candidate sky location probability fell within our observable field of view (0-45 deg zenith angle). We performed a search for a short timescale emission using 6 sliding time windows (dt = 0.3s, 1s, 3s, 10s, 30s and 100s), shifted forward in time by 20% of their width. We searched the 95% probability containment area in a timescale-dependent time period, from t0-5dt to t0+10dt, where t0 is the time of the GW trigger. No significant gamma-ray detection above the background was observed. The sensitivity of this analysis is greatly dependent on zenith angle, ranging from 3.2 deg to 45 deg for the area searched in this analysis. The 5sigma detection sensitivity to a 1s (100s) burst in the 80-800GeV energy range goes from 1.2e-06erg/cm^2 to 1.1e-04 erg/cm^2 (6.6e-06 erg/cm^2 to 5.0e-04 erg/cm^2), depending on the zenith angle. HAWC is a TeV gamma ray water Cherenkov array located in the state of Puebla, Mexico. It is sensitive to the energy range ~0.1-100TeV, and monitors 2/3 of the sky every day with an instantaneous field-of-view of ~2 sr. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25192 SUBJECT: LIGO/Virgo S190728q: One neutrino candidate from IceCube search DATE: 19/07/28 10:06:18 GMT FROM: Raamis Hussain at IceCube IceCube Collaboration (http://icecube.wisc.edu/) reports: A search for track-like muon neutrino events detected by IceCube consistent with the sky localization of gravitational-wave candidate S190728q in a time range of 1000 seconds [1] centered on the alert event time (2019-07-28 06:36:50.529 UTC to 2019-07-28 06:53:30.529 UTC) has been performed. During this time period IceCube was collecting good quality data. The search is a maximum likelihood analysis which searches for a generic point-like neutrino source coincident with the given GW skymap [2]. One track-like event is found in spatial and temporal coincidence with the gravitational-wave candidate S190728q calculated from the map circulated in the 4-Initial notice. This represents an overall p-value of 0.03 (1.84 sigma). An earlier search (GCN 25185) based on preliminary information of S190728q yielded no significant p-values for the worse GW localization [3]. Properties of the coincident events are shown below. dt ra (deg) dec (deg) Angular Uncertainty(deg) p-value(generic transient) ---------------------------------------------------------------------------------------------- -360 312.87 5.85 4.81 0.039 where: dt = Time offset (sec) of track event with respect to GW trigger. Angular uncertainty = Angular uncertainty of track event: the radius of a circle representing 90% CL containment by area. p-value = the p-value for this specific track event RA & Dec = Right ascension and declination in degrees quoted in J2000 epoch The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc@icecube.wisc.edu [1] Baret et al., Astroparticle Physics 35, 1 (2011) [2] Braun et al., Astroparticle Physics 29, 299 (2008) [3] GCN 25185: https://gcn.gsfc.nasa.gov/gcn3/25185.gcn3 //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25193 SUBJECT: LIGO/Virgo S190728q: No counterpart candidates in AGILE-MCAL observations DATE: 19/07/28 11:40:56 GMT FROM: Francesco Longo at U of Trieste,INFN Trieste F.Longo (Univ. Trieste, and INFN Trieste), M. Tavani (INAF/IAPS, and Univ. Roma Tor Vergata), F. Verrecchia, C. Pittori, F. Lucarelli (SSDC, and INAF/OAR), G.Piano, M. Cardillo, C. Casentini, A. Ursi (INAF/IAPS), A. Bulgarelli, V. Fioretti, N. Parmiggiani (INAF/OAS-Bologna), M. Pilia (INAF/OA-Cagliari), report on behalf of the AGILE Team: In response to the LIGO/Virgo GW event S190728q at T0 = 2019-07-28 06:45:10 (UT), a preliminary analysis of the AGILE minicalorimeter (MCAL) triggered data found no event candidates within a time interval covering -/+ 15 sec from the LIGO/Virgo T0. At the T0, about 100% of the S190728q 90 c.l. localization region was accessible to the AGILE MCAL. Three-sigma upper limits (ULs) are obtained for a 1 s integration time at different celestial positions within the accessible S190728q localization region, from a minimum of 1.63E-06 erg cm^-2 to a maximum of 2.59E-06 erg cm^-2 (assuming as spectral model a single power law with photon index 1.5). The AGILE-MCAL detector is a CsI detector with a 4 pi FoV, sensitive in the energy range 0.4-100 MeV. Additional analysis of AGILE data is in progress. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25194 SUBJECT: LIGO/Virgo S190728q : no neutrino counterpart candidate in ANTARES search DATE: 19/07/28 12:27:42 GMT FROM: Damien Dornic at CPPM,France M. Ageron (CPPM/CNRS), B. Baret (APC/CNRS), A. Coleiro (APC/Universite de Paris), M. Colomer (APC/Universite de Paris), D. Dornic (CPPM/CNRS), A. Kouchner (APC/Universite de Paris), 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 S190728q event using the 90% contour of the bayestar probability map provided by the GW interferometers (GCN#25187). The ANTARES visibility at the time of the alert, together with the 50% and 90% contours of the probability map are shown at http://antares.in2p3.fr/GW/S190728q.png . Considering the location probability provided by the LIGO/Virgo collaborations, there is a 38.1% chance that the GW emitter was in the ANTARES **upgoing** field of view at the time of the alert. No up-going muon neutrino candidate events were recorded in the ANTARES sky during a +/-500s time-window centered on the time 2019-07-28 06:45:10 and in the 90% contour of the S190728q event. The expected number of atmospheric background events in the region visible by ANTARES is 1.0e-04 in the +/- 500s time window. An extended search during +/- 1 hour gives no up-going muon neutrino coincidence. The expected number of atmospheric background events in the region visible by ANTARES is 7.4e-04 in this larger time window. ANTARES is the largest undersea neutrino detector, installed in the Mediterranean Sea, and it is primarily sensitive to neutrinos in the TeV-PeV energy range. At 10 TeV, the median angular resolution for muon neutrinos is about 0.5 degrees. In the range 1-100 TeV ANTARES has a competitive sensitivity to this position in the sky. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25195 SUBJECT: LIGO/Virgo S190728q: no counterpart candidates in AGILE-GRID observations DATE: 19/07/28 12:44:11 GMT FROM: Giovanni Piano at INAF-IAPS G. Piano (INAF/IAPS), F. Longo (Univ. Trieste, and INFN Trieste), M. Tavani (INAF/IAPS, and Univ. Roma Tor Vergata), F. Verrecchia, C. Pittori, F. Lucarelli (SSDC, and INAF/OAR), M. Cardillo, C. Casentini, A. Ursi (INAF/IAPS), A. Bulgarelli, V. Fioretti, N. Parmiggiani (INAF/OAS-Bologna), M. Pilia (INAF/OA-Cagliari), report on behalf of the AGILE Team: In response to the LIGO-Virgo GW event S190728q at T0 = 2019-07-28 06:45:10.547 UTC a preliminary analysis of the AGILE exposure at T0 shows that the Gamma-Ray Imaging Detector (GRID) exposure covered ~55% of the 90% c.l. localization region (LR). We performed an analysis of the GRID data in the energy range 50 MeV - 10 GeV near T0. No candidate gamma-ray transient was detected. The following preliminary GRID values of 3-sigma upper limits (ULs) are obtained: from 1.4e-06 to 4.0e-06 erg cm^-2 s^-1, with exposure of about 57% of the LR over the time interval (T0 - 2s; T0 + 2s); from 1.1e-06 to 3.2e-06 erg cm^-2 s^-1, with exposure of about 57% of the LR over the time interval (T0; T0 + 5s); from 4.6e-07 to 1.6e-06 erg cm^-2 s^-1, with exposure of about 57% of the LR over the time interval (T0; T0 + 10s); from 3.2e-08 to 4.4e-07 erg cm^-2 s^-1, with exposure of about 66% of the LR over the time interval (T0; T0 + 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: 25196 SUBJECT: LIGO/Virgo S190728q: Upper limits from Fermi-GBM Observations DATE: 19/07/28 13:09:00 GMT FROM: Rachel Hamburg at UAH R. Hamburg (UAH) reports on behalf of the Fermi-GBM Team and the GBM-LIGO/Virgo group: For the LIGO/Virgo detection of GW trigger S190728q (GCN 25187) and using the triple-detector BAYESTAR skymap, Fermi-GBM was observing 84.1% of the localization probability at event time. Approximately 15 min before the S190728q event, GBM triggered onboard to the short gamma-ray burst GRB 190728A (GCN 25181). However based on the large temporal offset and the difference in localization, this trigger is not considered a likely counterpart. An automated, blind search for short gamma-ray bursts below the onboard triggering threshold in Fermi-GBM also identified no counterpart candidates. The GBM targeted search, the most sensitive, coherent search for GRB-like signals, was run from +/- 30 s around merger time, and also identified no counterpart candidates. Part of the LVC localization region is behind the Earth for Fermi, located at RA = 129.9 and Dec = -11.1 with a radius of 67.5 degrees. We therefore set upper limits on impulsive gamma-ray emission for the LVC localization region visible to Fermi at merger time. Using the representative soft, normal, and hard GRB-like templates described in arXiv:1612.02395, we set the following 3 sigma flux upper limits over 10-1000 keV, weighted by GW localization probability, (in units of 10^-7 erg/s/cm^2): Timescale soft norm hard -------------------------------------- 0.128 s: 5.3 6.0 15.0 1.024 s: 2.0 2.7 4.2 8.192 s: 0.6 0.8 1.1 Assuming the median luminosity distance of 795 Mpc (z=0.165) from the GW detection, we estimate the following intrinsic luminosity upper limits over the 1 keV-10 MeV energy range (in units of 10^49 erg/s): Timescale soft norm hard -------------------------------------- 0.128 s: 6.2 6.4 27.0 1.024 s: 2.3 2.9 7.6 8.192 s: 0.7 8.6 2.0 //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25197 SUBJECT: LIGO/Virgo S190728q: Second update on neutrino search with IceCube DATE: 19/07/28 14:35:47 GMT FROM: Stefan Countryman at ICECUBE/Columbia U IceCube Collaboration (http://icecube.wisc.edu/) reports: This is an update of GCN 25192 including the p-value from the Bayesian search. Searches for track-like muon neutrino events detected by IceCube consistent with the sky localization of gravitational-wave candidate S190728q in a time range of 1000 seconds [1] centered on the alert event time (2019-07-28 06:36:50.529 UTC to 2019-07-28 06:53:30.529 UTC) have been performed. During this time period IceCube was collecting good quality data. Two hypothesis tests were conducted. The first search is a maximum likelihood analysis which searches for a generic point-like neutrino source coincident with the given GW skymap [2]. The second uses a Bayesian approach to quantify the joint GW + neutrino event significance, which assumes a binary merger scenario and accounts for known astrophysical priors in the significance estimate, such as GW source distance [3]. One track-like event is found in spatial and temporal coincidence with the gravitational-wave candidate S190728q calculated from the map circulated in the 4-Initial notice. This represents an overall p-value of 0.03 (1.84 sigma) from the generic transient search and an overall p-value of 0.013 (2.22 sigma) for the Bayesian search. These p-values measure the consistency of the observed track-like events with the known atmospheric backgrounds. An earlier search (GCN 25185) based on preliminary information of S190728q yielded no significant p-values for the worse GW localization. The reported p-values can differ due to the estimated distance of the GW candidate. The distance is used as a prior in Bayesian binary merger search, while it is not taken into account in the generic transient point-like source search. Properties of the coincident events are shown below. dt|ra (deg)|dec (deg)|Angular Uncertainty(deg)|p-value (bayesian)|p-value(generic transient) -----+--------+---------+------------------------+------------------+-------------------------- -360|312.87 |5.85 |4.81 |0.013 |0.039 where: dt = Time offset (sec) of track event with respect to GW trigger. Angular uncertainty = Angular uncertainty of track event: the radius of a circle representing 90% CL containment by area. p-value = the p-value for this specific track event from each search. RA & Dec = Right ascension and declination in degrees quoted in J2000 epoch The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc@icecube.wisc.edu [1] Baret et al., Astroparticle Physics 35, 1 (2011) [2] Braun et al., Astroparticle Physics 29, 299 (2008) [3] Bartos et al. arXiv:1810.11467 (2018) and Countryman et al.arXiv:1901.05486 (2019) //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25198 SUBJECT: LIGO/Virgo S190728q: No counterpart candidates in Fermi-LAT observations DATE: 19/07/28 15:01:03 GMT FROM: Milos Kovacevic at INFN Perugia M. Kovacevic (INFN Perugia), M. Axelsson (KTH and Stockholm Univ.), F. Longo (Univ. and INFN, Trieste) and D. Kocevski (NASA/GSFC) report on behalf of the Fermi-LAT Collaboration: We have searched data collected by the Fermi Large Area Telescope (LAT) on July 28, 2019, for possible high-energy (E > 100 MeV) gamma-ray emission in spatial/temporal coincidence with the LIGO/Virgo trigger S190728q (GCN 25187). We define "instantaneous coverage" as the integral over the region of the LIGO probability map that is within the LAT field of view at a given time, and "cumulative coverage" as the integral of the instantaneous coverage over time. Fermi-LAT had instantaneous coverage of ~58% of the LIGO probability region at the time of the trigger (T0 = 2019-07-28 06:45:10.529 UTC), and reached ~95% coverage around T0+5.8ks. The remaining area was not observed within 10ks of the burst. We performed a search for a transient counterpart within the observed region of the 90% contour of the LIGO map in a fixed time window from T0 to T0+10 ks. No significant 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, and no additional excesses were found. Energy flux upper bounds for the fixed time interval between 100 MeV and 1 GeV for this search vary between 2.3E-10 and 2.7E-08 [erg/cm^2/s]. The Fermi-LAT point of contact for this event is Milos Kovacevic (milos.kovacevic@pg.infn.it). 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. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25199 SUBJECT: LIGO/Virgo S190728q: Optical Candidate from the Zwicky Transient Facility ZTF19abjethn DATE: 19/07/28 15:06:42 GMT FROM: Mansi M. Kasliwal at Caltech/Carnegie Mansi M. Kasliwal (Caltech), Leo P. Singer (NASA GSFC), Eric C. Bellm (UW), Michael W. Coughlin (Caltech), Daniel A. Perley (LJMU), Jesper Sollerman (OKC), Igor Andreoni (Caltech), Erik Kool (OKC), Danny Goldstein (Caltech), Rahul Biswas (OKC), Richard Walters (Caltech), Varun Bhalerao (IITB), G. C. Anupama (IIA), Shreya Anand (Caltech), Tomas Ahmuda (UMD), Brad Cenko (NASA GSFC), Sara Webb (Swinburne), Jeff Cooke (Swinburne), Kirsty Taggart (LJMU), Sudhanshu Barway (IIAP), Alessandra Corsi (TTU), Mattia Bulla (OKC), Albert Kong (Taiwan), Chris Copperwheat (LJMU) On behalf of the Zwicky Transient Facility (ZTF) and Global Relay of Observatories Watching Transients Happen (GROWTH) collaborations We observed the localization region of the gravitational wave trigger S190728q (GCN 25187) with the Palomar 48-inch telescope equipped with the 47 square degree ZTF camera (Bellm et al. 2019, Graham et al. 2019). A new tiling was automatically optimally determined and triggered using the GROWTH Target of Opportunity marshal (Coughlin et al. 2019a, Kasliwal et al. 2019b). We enclosed 64% of the probability and obtained a sequence of 300s exposures in g-band, r-band and g-band before sunrise. The images were processed through the ZTF reduction and image subtraction pipelines at IPAC to search for potential counterparts (Masci et al. 2019). We applied standard filtering criterion including rejecting stellar sources (Tachibana and Miller 2018) and moving objects and applying machine learning algorithms (Mahabal et al. 2019, Duev et al. 2019). A promising candidate with the first detection after the GW merger time and a fast intra-night rise in both filters is: ------------------------------------------------------------------------------------------------------------------- ZTF Name | RA (deg) | DEC (deg) | Filter | Mag | Magerr | Filter | Mag | Magerr -------------------------------------------------------------------------------------------------------------------- ZTF19abjethn | 326.395431 | 20.690590 | r | 19.65 | 0.11 | g | 19.82 | 0.16 -------------------------------------------------------------------------------------------------------------------- We reported this candidate to TNS and it was given the name AT2019lvs. The candidate is offset from a galaxy with SDSS phot-z estimate of 0.228 ± 0.0286. We serendipituously observed this field the previous night with ZTF and did not detect the candidate. Additional analysis and continued follow-up is in progress and encouraged. ZTF and GROWTH are worldwide collaborations comprising Caltech, USA; IPAC, USA, WIS, Israel; OKC, Sweden; JSI/UMd, USA; U Washington, USA; DESY, Germany; MOST, Taiwan; UW Milwaukee, USA; LANL USA; Tokyo Tech, Japan; IIT-B, India; IIA, India; LJMU, UK; TTU, USA; and USyd, Australia. ZTF acknowledges the generous support of the NSF under AST MSIP Grant No 1440341. GROWTH acknowledges generous support of the NSF under PIRE Grant No 1545949. Alert distribution service provided by DIRAC@UW (Patterson et al. 2019). Alert filtering and follow-up co-ordination is being undertaken by the GROWTH marshal system (Kasliwal et al. 2019). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25200 SUBJECT: LIGO/Virgo S190728q: No counterpart candidates in the Swift/BAT Observations DATE: 19/07/28 16:02:40 GMT FROM: Amy Lien at GSFC A. Y. Lien (GSFC/UMBC), S. D. Barthelmy (NASA/GSFC), D. M. Palmer (LANL), T. Sakamoto (AGU), A. P. Beardmore (U. Leicester), M. G. Bernardini (INAF-OAB), A. A. Breeveld (MSSL-UCL), 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 (ASI-SSDC), S. Emery (UCL-MSSL), P. A. Evans (U. Leicester), P. Giommi (ASI), C. Gronwall (PSU), D. Hartmann (Clemson U.), J. A. Kennea (PSU), H. A. Krimm (NSF), N. P. M. Kuin (UCL-MSSL), F. E. Marshall (NASA/GSFC), A. Melandri (INAF-OAB), 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. J. Page (UCL-MSSL), M. Perri (ASDC), J. L. Racusin (NASA/GSFC), B. Sbarufatti (INAF-OAB/PSU), M. H. Siegel (PSU), G. Tagliaferri (INAF-OAB), A. Tohuvavohu (PSU), 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 S190728q (LIGO/VIRGO Collaboration GCN Circ. 25187), where T0 is the LVC trigger time (2019-07-28T06:45:10.529 UTC). The center of the BAT FOV at T0 is RA = 292.028 deg, DEC = 19.556 deg, and the ROLL angle is 328.234 deg. The BAT Field of View (>10% partial coding) covers 72.15% of the integrated LVC localization probability, and 70.71% of the galaxy convolved probability (Evans et al. 2016). 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. 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 ~ 8.82 x 10^-8 erg/s/cm^2. No event data are available within T0 +/- 100 s. BAT retains decreased, but significant, sensitivity to rate increases for gamma-ray events outside of its FOV. About 15.93% 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 higher than those within the FOV. The results of the BAT analysis are available at https://swift.gsfc.nasa.gov/results/BATbursts/team_web/S190728q/web/source.html //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25201 SUBJECT: LIGO/Virgo S190728q: Photometric Redshift and Stellar Mass Estimates for the Potential Host Galaxy of Optical Counterpart Candidate ZTF19abjethn DATE: 19/07/28 16:04:04 GMT FROM: Daniel Goldstein at Caltech Rongpu Zhou (U. Pittsburgh), Jeff Newman (U. Pittsburgh), Danny Goldstein (Caltech), Mansi M. Kasliwal (Caltech) On behalf of the Zwicky Transient Facility (ZTF) and Global Relay of Observatories Watching Transients Happen (GROWTH) collaborations Using photometry from the Dark Energy Camera Legacy Survey (DECaLS; Dey et al. 2019) Data Release 7 (DR7), we have estimated the photometric redshift of SDSS J214534.52+204130.6, a possible host galaxy of ZTF19abjethn (GROWTH Collaboration 2019; GCN 25199), an optical counterpart candidate to the gravitational wave trigger S190728q (The LIGO Scientific Collaboration and the Virgo Collaboration 2019; GCN 25187). This photometric redshift has been determined by applying a random forest algorithm to the DR7 photometry (including both magnitude and size information) combined with spectroscopic redshifts from a variety of sources. Zhou et al. 2019 (in prep.) will provide a full description of the algorithm used. The object was only observed once in the g band for DR7, but photometry nevertheless appears reasonable. The stellar mass of the host has been estimated via a random forest algorithm applied to the DECaLS DR7 photometry, trained using masses from the S82-MGC stellar mass catalog from Bundy et al. (2015). The reconstructed masses in general agree with S82-MGC masses to better than 0.15 dex, even though independent photometry is being used for each; we take 0.20 dex as an upper limit on systematics (apart from assumed initial mass function, which can have effects of up to 0.5 dex). Statistical errors on the mass have been propagated from the photometric redshift uncertainty (which dominates over photometric errors). ----------------------------------------------------------------------------------------------- Name | RA (deg) | DEC (deg) | z_phot | z_phot_err |log10( M_* ) [Msun] | M_* err [log10 Msun] --------------------------+----------------+--------------+--------+------------+--------------------+---------------------- SDSS J214534.52+204130.6 | 326.393869200 | 20.691841120 | 0.236 | 0.023 | 11.09 | 0.11 (stat), <0.20 (sys) ----------------------------------------------------------------------------------------------- The host appears to be a modestly massive early-type galaxy in Legacy Survey imaging. There is a cluster of galaxies of similar color centered nearby, at (RA, dec) of 326.47, 20.71. Assuming a Planck Collaboration et al. (2015) cosmology, the values imply a luminosity distance to the event of 1.18 Gpc, which is within 2 standard deviations of the value inferred from the gravitational wave signal (The LIGO Scientific Collaboration and the Virgo Collaboration 2019; GCN 25187). Adopting the value of H0 from Riess et al. (2019) would imply a luminosity distance of 1.03 Gpc, which is consistent with the LIGO distance to within roughly 1 standard deviation. The photometric redshift estimate presented here is highly consistent with the value from SDSS (0.228 +/- 0.029, as reported in GCN 25199). Development of the photometric redshifts and stellar mass estimates used here was funded by the U.S. Department of Energy Office of Science to facilitate target selection for the DESI survey. ZTF and GROWTH are worldwide collaborations comprising Caltech, USA; IPAC, USA, WIS, Israel; OKC, Sweden; JSI/UMd, USA; U Washington, USA; DESY, Germany; MOST, Taiwan; UW Milwaukee, USA; LANL USA; Tokyo Tech, Japan; IIT-B, India; IIA, India; LJMU, UK; TTU, USA; and USyd, Australia. ZTF acknowledges the generous support of the NSF under AST MSIP Grant No 1440341. GROWTH acknowledges generous support of the NSF under PIRE Grant No 1545949. Alert distribution service provided by DIRAC@UW (Patterson et al. 2019). Alert filtering and follow-up co-ordination is being undertaken by the GROWTH marshal system (Kasliwal et al. 2019). This message may be cited. -- Danny Goldstein http://astro.caltech.edu/~danny //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25202 SUBJECT: LIGO/Virgo S190728q: Identification of a Faint Blue Static Source at the Location of ZTF19abjethn DATE: 19/07/28 17:39:13 GMT FROM: Daniel Goldstein at Caltech Danny Goldstein (Caltech), Erik Kool (OKC), Jeff Newman (U. Pittsburgh), Rongpu Zhou (U. Pittsburgh), Mansi M. Kasliwal (Caltech), Igor Andreoni (Caltech), Daniel A. Perley (LJMU), Michael W. Coughlin (Caltech) On behalf of the Zwicky Transient Facility (ZTF) and Global Relay of Observatories Watching Transients Happen (GROWTH) collaborations ZTF19abjethn (GROWTH Collaboration 2019; GCN 25199), an optical counterpart candidate to the gravitational wave trigger S190728q (The LIGO Scientific Collaboration and the Virgo Collaboration 2019; GCN 25187), is spatially coincident (to within less than one arcsecond) with a faint blue static source. The source is detected only marginally in DECam Legacy Survey (DECaLS) and SDSS imaging thus we are unable to estimate a photometric redshift or stellar mass for the potential host, assuming the source is a galaxy; we are also unable to determine if the source is a star or a galaxy. The source has the following magnitudes in DECaLS DR7: ----------------------------------------------------------------------------------------------- Name | RA (deg) | DEC (deg) | Filter | Mag | Magerr | Filter| Mag | Magerr | Filter | Mag | Magerr | Filter --------------+-------------+-------------+--------+-------+---------+-------+-------+--------- SDSS J214534.91+204126.2 | 326.395467148 | 23.456085 | 0.07854421 | g | 23.09552 | 0.07489753 | r | 23.554304 | 0.36628282 | z ----------------------------------------------------------------------------------------------- Spectroscopic follow-up is encouraged. ZTF and GROWTH are worldwide collaborations comprising Caltech, USA; IPAC, USA, WIS, Israel; OKC, Sweden; JSI/UMd, USA; U Washington, USA; DESY, Germany; MOST, Taiwan; UW Milwaukee, USA; LANL USA; Tokyo Tech, Japan; IIT-B, India; IIA, India; LJMU, UK; TTU, USA; and USyd, Australia. ZTF acknowledges the generous support of the NSF under AST MSIP Grant No 1440341. GROWTH acknowledges generous support of the NSF under PIRE Grant No 1545949. This message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25203 SUBJECT: LIGO/Virgo S190728q: declination for GCN 25202 DATE: 19/07/28 18:05:04 GMT FROM: Daniel Goldstein at Caltech Danny Goldstein (Caltech) GCN 25202 neglected to include the declination of the static source coincident with ZTF19abjethn. The corrected data are as follows: ----------------------------------------------------------------------------------------------- Name | RA (deg) | DEC (deg) | Filter | Mag | Magerr | Filter| Mag | Magerr | Filter | Mag | Magerr | Filter --------------+-------------+-------------+--------+-------+---------+-------+-------+--------- SDSS J214534.91+204126.2 | 326.395467148 | 20.690611120 | 23.456085 | 0.07854421 | g | 23.09552 | 0.07489753 | r | 23.554304 | 0.36628282 | z ----------------------------------------------------------------------------------------------- Apologies for any confusion this may have caused. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25204 SUBJECT: LIGO/Virgo S190728q: Pan-STARRS detection of the transient AT2019lvs/ZTF19abjethn 18hrs before S190728q DATE: 19/07/28 18:13:31 GMT FROM: Stephen Smartt at Queen's U/Belfast S. J. Smartt, K. W. Smith (QUB), M. Huber, K. Chambers (IfA), D. R. Young, S. Srivastav, O. McBrien, J. Gillanders, D. O'Neil, P. Clark, S. Sim (QUB), T. de Boer, J. Bulger, J. Fairlamb, C.-C. Lin, T. Lowe, E. Magnier A. Schultz, R. J. Wainscoat, M. Willman (IfA, University of Hawaii), A. Rest (STScI), C. Stubbs (Harvard) We imaged part of the localisation map of the gravitational wave S190728q (GCN 25187) with Pan-STARRS1 (Chambers et al. 2016, arXiv:1612.05560C) on the night preceding the detection (GW detection at 58692.28137188518) during routine survey observations. This coverage included the location of the ZTF reported optical transient AT2019lvs (ZTF19abjethn; Kasliwal et al. GCN 25199). Pan-STARRS observed in the NEO sequence of 45s x 4 in the wide gri-composite filter w-band. Images were processed with the IPP (Magnier et al. 2016, arXiv:1612.05240) and the w-band reference sky frame was subtracted during normal processing. We detected a transient source (PS19dwa) in all four difference images. In 2 images it is formally below 5-sigma but visually detected. The 2 other images have 5-sigma detections at AB magnitudes : MJD w w_err 58691.544552 22.27 0.22 58691.531772 22.01 0.20 At position: RA = 326.39543 (21:45:34.90) DEC = +20.69064 (+20:41:26.3) This is coincident with the ZTF coordinates to 0.2 arcsec, and hence is almost certainly the same object. Therefore this optical transient is detected 18 hours before S190728q. There are no other detections of transient flux at this position in about 30 epochs of Pan-STARRS grizy imaging over the last 2000 days in our detection database. AT2019lvs is coincident with a blue source (SDSS J214534.91+204126.2) in SDSS and Pan-STARRS and DECaLs (Dey et al. 2019, DR7 as reported in Zhou et al. GCN 25201). The object is detected only in the g-band in SDSS and PS1 surveys (SDSS g = 22.57 +/- 0.14). It is uncertain if it is stellar or a faint blue galaxy in all three surveys. It is more likely to be associated with this faint source than the brighter host at photoz - 0.23 reported by Zhou et al. (GCN 25201) and Kasliwal et al. (GCN 25199). A foreground variable or CV is the most likely explanation, but a more exotic explanation and association with S190728q can't be ruled out and a classification or redshift is essential. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25206 SUBJECT: LIGO/Virgo S190728q: LCO Follow-Up of ZTF19abjethn (AT2019lvs) DATE: 19/07/28 20:43:25 GMT FROM: Michael Coughlin at Caltech/LIGO Tomas Ahumada (UMD) and Michael W. Coughlin (Caltech) on behalf of the Global Relay of Observatories Watching Transients Happen (GROWTH) collaboration. We used the 2-m telescope at the LCO node at Haleakala Observatory to obtain 180 second g,r, and i-band images for the ZTF optical transient ZTF19abjethn (AT2019lvs) listed in Kasliwal et al. (GCN 25199) starting at 14:50:26.164 UT on 2019-07-28. The measurements of this transient are consistent with a significant rise in the r-and g-band magnitudes reported by both Kasliwal et al. (GCN 25199), on top of the rise reported by Smartt et al. (GCN 25204), albeit in a different band. Magnitudes are derived after calibrating against PS1: u = 18.4 +- 0.1 g = 17.38 +- 0.03 r = 17.51 +- 0.04 i = 17.62 +- 0.04 //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25207 SUBJECT: LIGO/Virgo S190728q: ZTF19abjethn is inconsistent with new GW localization DATE: 19/07/28 20:51:28 GMT FROM: Mansi M. Kasliwal at Caltech/Carnegie Mansi M. Kasliwal (Caltech), Igor Andreoni (Caltech) and Michael Coughlin (Caltech) On behalf of the Zwicky Transient Facility (ZTF) and Global Relay of Observatories Watching Transients Happen (GROWTH) collaborations The new skymap just released by LIGO/Virgo (Lalinference.offline.fits.gz) suggests that ZTF19abjethn (GCN 25199) is now outside the 95% confidence level in the updated localization contour. We retract this candidate as a potential counterpart of S190728q (GCN 25187). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25208 SUBJECT: LIGO/Virgo S190728q: Update on Sky-Localization and Source-Classification DATE: 19/07/28 21:54:44 GMT FROM: Sarah Antier at APC The LIGO Scientific Collaboration and Virgo Collaboration report: We have conducted further analysis of the LIGO and Virgo data around the time of the compact binary coalescence (CBC) candidate S190728q (GCN 25187). Parameter estimation has been performed using LALInference [1] and a new sky map, LALInference.offline.fits.gz, distributed via GCN Notice, is available for retrieval from the GraceDB event page: https://gracedb.ligo.org/superevents/S190728q/ LALInference.offline.fits.gz is the preferred sky map at this time. The 90% credible region is 104 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 874 +/- 171 Mpc (a posteriori mean +/- standard deviation). Based on posterior support from parameter estimation [1,2], under the assumption that the candidate S190728q is astrophysical in origin, there is strong evidence against the hypothesis that the lighter compact object has a mass < 3 solar masses (HasNS < 1%) and a negligible probability of having disrupted material outside the final compact object (HasRemnant < 1%). The parameter estimation based classification of the GW signal, in order of descending probability, is BBH (95%), MassGap (5%), NSBH (<1%), or BNS (<1%). The above mentioned probabilities are based on full exploration of the binary parameter space, and hence are the preferred classification results that supersede the ones stated in GCN 25187. The probability of non-astrophysical origin and the false alarm rate are not being updated at this time; both measures of significance should be expected to change with offline analyses and continued observations. For further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo Public Alerts User Guide . [1] Veitch, et al. PRD 91, 042003 (2015) [2] Abbott, et al. PRL 116, 241102 (2016) //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25209 SUBJECT: LIGO/Virgo S190728q: Classification of AT2019lvs/ZTF19abjethn as a CV DATE: 19/07/28 22:01:16 GMT FROM: Kate Maguire at Trinity College Dublin Mark Magee (TCD), Kate Maguire (TCD), Manuel Torres (IAC), Peter Jonker (SRON/Radboud University), Morgan Fraser (UCD) report on behalf of the GW@WHT collaboration: We obtained an optical spectrum of the transient AT2019lvs/ZTF19abjethn discovered by ZTF (Kasliwal et al. GCN 25199) within the original probability map of S190728q (GCN 25187) but not the updated one released in GCN/LVC NOTICE on Sun 28 Jul 19 20:29:15 UT (see also GCN 25207). The spectrum was obtained on 2019 July 28 21:40 UT using the ACAM instrument mounted on the William Herschel Telescope located on the Roque de Los Muchachos Observatory, La Palma, Spain. The spectrum shows Balmer series emission at z=0 consistent with a cataclysmic variable. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25210 SUBJECT: LIGO/Virgo S190728q: Third update on neutrino search with IceCube DATE: 19/07/28 22:28:20 GMT FROM: Raamis Hussain at IceCube IceCube Collaboration (http://icecube.wisc.edu/) reports: This is an update of GCN 25197 including updated p-values for the map circulated in the 5-Update GCN notice. Searches for track-like muon neutrino events detected by IceCube consistent with the sky localization of gravitational-wave candidate S190728q in a time range of 1000 seconds [1] centered on the alert event time (2019-07-28 06:36:50.529 UTC to 2019-07-28 06:53:30.529 UTC) have been performed. During this time period IceCube was collecting good quality data. Two hypothesis tests were conducted. The first search is a maximum likelihood analysis which searches for a generic point-like neutrino source coincident with the given GW skymap [2]. The second uses a Bayesian approach to quantify the joint GW + neutrino event significance, which assumes a binary merger scenario and accounts for known astrophysical priors in the significance estimate, such as GW source distance [3]. One track-like event is found in spatial and temporal coincidence with the gravitational-wave candidate S190728q calculated from the map circulated in the 5-Update notice. This represents an overall p-value of 0.014 (2.21 sigma) from the generic transient search and an overall p-value of 0.010 (2.33 sigma) for the Bayesian search. These p-values measure the consistency of the observed track-like events with the known atmospheric backgrounds. The reported p-values can differ due to the estimated distance of the GW candidate. The distance is used as a prior in Bayesian binary merger search, while it is not taken into account in the generic transient point-like source search. Properties of the coincident events are shown below. dt|ra (deg)|dec (deg)|Angular Uncertainty(deg)|p-value (bayesian)|p-value(generic transient) -----+--------+---------+------------------------+------------------+-------------------------- -360|312.87 |5.85 |4.81 |0.010 |0.016 where: dt = Time offset (sec) of track event with respect to GW trigger. Angular uncertainty = Angular uncertainty of track event: the radius of a circle representing 90% CL containment by area. p-value = the p-value for this specific track event from each search. RA & Dec = Right ascension and declination in degrees quoted in J2000 epoch The IceCube Neutrino Observatory is a cubic-kilometer neutrino detector operating at the geographic South Pole, Antarctica. The IceCube realtime alert point of contact can be reached at roc@icecube.wisc.edu [1] Baret et al., Astroparticle Physics 35, 1 (2011) [2] Braun et al., Astroparticle Physics 29, 299 (2008) [3] Bartos et al. arXiv:1810.11467 (2018) and Countryman et al.arXiv:1901.05486 (2019) //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25212 SUBJECT: LIGO/Virgo S190728q: ZTF19abjethn TShAO and NUTTelA-TAO optical observations / classification DATE: 19/07/29 01:03:07 GMT FROM: Alexei Pozanenko at IKI, Moscow S. Belkin (IKI), I. Reva (AFIF), M. Krugov (AFIF), A. Pozanenko (IKI), B. Grossan (ECL) report on behalf of larger GRB IKI FuN collaboration: We observed the optical transient AT2019lvs/ZTF19abjethn discovered by ZTF (Kasliwal et al. GCN 25199) with TShAO Zeiss-1000 and CDK700 telescope (NUTTelA-TAO) of Assy-Turgen observatory. Observations started earlier than Update on Sky-Localization (LVC, GCN 25208). We observed the transient in B,R - filters. The transient photometry is following. Date, UTC, MJD, Filter, Exposure, OT, Err, Uplim, FWHM Obs., Telescope 2019-07-28 16:04:19 58692.65864 R 23*120 16.63 0.02 21.5 2.1 TSHAO Zeiss-1000 2019-07-28 17:15:10 58692.72234 R 5*120 16.49 0.03 21.3 1.8 Assy-Turgen CDK700 2019-07-28 17:17:18 58692.72729 B 10*120 16.35 0.07 21.0 1.8 Assy-Turgen CDK700 2019-07-28 20:29:12 58692.86056 B 10*120 15.51 0.09 21.0 2.8 Assy-Turgen CDK700 The photometry is based on the nearby USNO-B1 (R2) stars. The extremely blue color of the transient (B-R) = -0.15 is fully agreed with classification of the transient as CV (Magee et al., GCN 25209). //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25213 SUBJECT: LIGO/Virgo S190728q: No counterpart candidates in KAIT observations DATE: 19/07/29 03:05:42 GMT FROM: Weikang Zheng at UC Berkeley Keto D. Zhang, Andrew Hoffman, Shaunak Modak, Thomas de Jaeger, James Sunseri, Yukei Murakami, WeiKang Zheng, Benjamin Stahl, and Alexei V. Filippenko (UC Berkeley) report on behalf of Lick/KAIT GW follow-up team: The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at Lick Observatory, observed the 90% region of the gravitational-wavei event S190728q (GCN 25187) detected by LIGO/Virgo. More than one thousand galaxies were selected from the Glade catalog V1.0 (Dalya et al., 2018, MNRAS, 479, 2374; http://aquarius.elte.hu/glade/) according to their priority score. KAIT observed 90 of them based on their priority scores and elevation visibility, with each clear-filter exposure time being 60 s. The first image was taken at 08:55:35, July 28th UT, about 2.17 hours after the trigger, and the last image at 12:10:36 UT. Our typical limiting mag is 19.0. No viable counterparts were identified and the analysis is ongoing. A full list of galaxies observed by KAIT is given below. GladeID UT(July20) RA_J2000 Dec_J2000 ----------------------------------------------- G0236749 08:55:35 00:46:32.0078 +36:19:31.8972 G1023167 08:57:20 20:07:32.9297 -03:33:22.1148 G0905906 08:58:32 20:08:32.7026 -09:39:24.642 G0480402 08:59:41 20:09:32.8272 -09:08:46.3272 G1255471 09:00:50 20:12:16.692 -08:54:07.254 G0476578 09:02:00 20:14:33.523 -08:27:53.3772 G0149230 09:03:11 20:16:11.5502 -03:45:40.7916 G0439598 09:04:24 20:43:57.3048 +06:06:35.0028 G1406085 09:05:34 20:44:26.9018 +07:13:14.574 G1258469 09:06:43 20:46:50.7494 +08:50:41.01 G1248314 09:07:52 20:47:20.713 +05:40:54.0048 G0935153 09:09:02 20:47:29.6191 +09:24:06.9264 G1385959 09:10:11 20:47:44.0258 +09:55:53.9148 G1069077 09:11:20 20:47:58.6303 +06:23:52.2024 G0691529 09:12:30 20:48:10.2466 +07:00:59.1948 G0170309 09:13:39 20:49:02.3438 +06:45:15.228 G0992709 09:14:48 20:49:02.527 +04:50:16.1304 G1163136 09:15:58 20:49:13.1251 +08:38:37.2084 G0261631 09:17:07 20:49:13.3008 +05:33:47.0484 G0218951 09:18:16 20:51:14.934 +06:05:54.6576 G0192870 09:19:26 20:51:29.209 +05:25:38.658 G0329085 09:20:35 20:52:48.0322 +09:58:34.4784 G0953363 09:21:44 20:52:51.8189 +06:59:25.4976 G1022213 09:22:53 20:53:06.9434 +10:05:32.6868 G1039531 09:24:03 20:53:14.9194 +06:07:48.7236 G1379283 09:25:12 20:53:17.0069 +10:37:26.7312 G0401694 09:26:23 20:53:22.1338 +05:25:43.5684 G1410599 09:27:35 20:53:58.0445 +10:24:23.9616 G0335395 09:28:44 20:54:03.955 +07:13:44.9904 G0201390 09:29:53 20:54:04.5043 +08:02:35.9916 G0860377 10:08:00 20:54:21.2402 +06:17:09.2148 G1294503 10:09:09 20:54:26.4038 +05:01:57.2916 G0201635 10:10:18 20:54:51.1889 +07:57:13.1976 G1106635 10:11:28 20:55:16.3404 +05:46:24.816 G1289462 10:12:41 20:55:30.7104 +10:22:18.03 G0169160 10:13:52 20:55:36.0864 +05:22:42.3012 G0373718 10:15:02 20:55:46.333 +07:13:06.2652 G1344558 10:16:11 20:55:57.2681 +10:29:33.2916 G1476964 10:17:21 20:55:59.839 +12:08:12.0552 G0844170 10:18:30 20:56:00.2198 +08:15:01.2996 G0295104 10:19:37 20:56:21.0938 +09:17:19.9176 G1164188 10:20:47 20:56:37.7563 +12:16:00.2532 G1227822 10:21:56 20:56:49.9512 +13:04:25.2876 G0601857 10:23:03 20:57:18.7939 +12:11:13.6032 G1339441 10:24:13 20:57:38.5034 +10:24:32.292 G0523320 10:25:22 20:57:56.5356 +06:04:22.512 G1128719 10:26:31 20:58:01.56 +08:30:10.9224 G0960770 10:27:40 20:58:01.8384 +10:00:02.9232 G0195999 10:28:50 20:58:12.942 +10:07:23.9376 G1355518 10:29:59 20:58:14.9122 +08:25:38.9388 G1307621 10:31:08 20:58:19.0063 +06:51:04.9392 G1273242 10:32:18 20:58:45.6151 +09:30:09.9936 G0839466 10:33:31 20:58:53.8769 +13:50:54.6396 G1346841 10:34:41 20:58:55.7299 +10:34:42.9816 G1140068 10:35:50 20:59:23.3057 +12:10:37.9812 G1095715 10:37:01 20:59:24.2066 +05:49:13.7496 G0964188 10:38:12 20:59:24.961 +10:53:23.064 G0574494 10:39:22 21:00:06.3427 +09:55:56.5788 G0860425 10:40:31 21:00:21.5551 +07:45:47.5632 G1146620 10:41:40 21:00:32.124 +10:03:39.9348 G1346944 11:37:03 21:00:33.0761 +09:25:51.9348 G0846026 11:38:13 21:00:39.7558 +08:14:21.9372 G1080012 11:39:22 21:01:01.0034 +12:11:04.3728 G1422051 11:40:31 21:01:10.7446 +12:27:34.398 G0932932 11:41:41 21:01:30.8496 +11:30:03.5928 G1111413 11:42:50 21:01:37.5 +10:15:56.5956 G0778389 11:43:57 21:02:39.0235 +10:49:30.0216 G1012503 11:45:07 21:02:48.6401 +13:08:10.878 G0757614 11:46:16 21:02:57.7368 +10:10:38.5968 G0809046 11:47:25 21:02:58.8355 +10:33:00.5976 G0852728 11:48:34 21:03:25.2101 +14:33:19.3572 G0904365 11:49:44 21:03:51.4747 +11:45:49.4892 G1297650 11:50:53 21:03:58.1837 +13:08:29.13 G1188076 11:52:02 21:04:04.5482 +11:18:48.4956 G0994698 11:53:16 21:04:08.1811 +14:42:15.1668 G0373310 11:54:25 21:04:15.791 +10:33:25.47 G0804854 11:55:35 21:04:37.163 +09:42:57.6792 G0873177 11:56:44 21:04:50.7641 +11:52:38.856 G1293574 11:57:53 21:04:50.9179 +12:55:38.8632 G1284258 11:59:02 21:05:06.8042 +13:34:37.6572 G0311386 12:00:12 21:05:15.0514 +12:10:32.6928 G1449742 12:01:21 21:05:16.6478 +11:24:56.1312 G0110246 12:02:30 21:05:18.9698 +12:59:59.7048 G0527283 12:03:40 21:05:23.5841 +15:05:58.7112 G0892624 12:04:49 21:05:25.6274 +11:22:41.1528 G0191566 12:05:58 21:05:45.498 +07:57:56.826 G0326509 12:07:08 21:05:46.5454 +09:36:39.1284 G0403282 12:08:17 21:05:57.715 +13:35:19.1652 G1332587 12:09:26 21:06:02.9297 +13:28:21.1908 G0401046 12:10:36 21:06:12.107 +13:41:25.2276 //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25214 SUBJECT: LIGO/Virgo S190728q: No transient candidates in CALET observations DATE: 19/07/29 03:15:53 GMT FROM: Yuta Kawakubo at Louisiana State U./CALET S. Nakahira (RIKEN), A. Yoshida, T. Sakamoto, V. Pal'shin, S. Sugita (AGU), Y. Kawakubo (LSU), K. Yamaoka (Nagoya U), Y. Asaoka, S. Ozawa, S. Torii (Waseda U), Y. Shimizu, T. Tamura (Kanagawa U), N. Cannady (GSFC/UMBC), M. L. Cherry (LSU), S. Ricciarini (U of Florence), P. S. Marrocchesi (U of Siena), and the CALET collaboration: The CALET Gamma-ray Burst Monitor (CGBM) was operating at the trigger time of S190728q T0 = 2019-07-28 06:45:10.529 UT (The LIGO Scientific Collaboration and Virgo Collaboration, GCN Circ. 25187). No CGBM on-board trigger occurred around the event time. Based on the LIGO-Virgo localization sky map, the summed LIGO probabilities inside the CGBM HXM (7 - 3000 keV) and SGM (40 keV - 28 MeV) fields of view are 0 % and 0 %, respectively (and 0 % credible region of the initial localization map was above the horizon). The HXM and SGM fields of view were centered at RA = 175.7 deg, Dec = 36.7 deg and RA = 184.9 deg, Dec = 30.3 deg at T0, respectively. The CALET Calorimeter (CAL) was operating in the low energy trigger mode at the trigger time of S190728q, but the CAL FOV does not have any overlap with LVC probability significance map. The CAL FOV was centered at RA= 184.8 deg, DEC= 30.3 deg at T0. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25215 SUBJECT: LIGO/Virgo S190728q: Optical Counterpart Candidates from DECam-GROWTH DATE: 19/07/29 06:55:42 GMT FROM: Daniel Goldstein at Caltech Danny Goldstein (Caltech), Igor Andreoni (Caltech), Mansi M. Kasliwal (Caltech), Shreya Anand (Caltech), Erik Kool (OKC), Sara Webb (Swinburne), Ashot Bagdasaryan (Caltech), Dmitry Duev (Caltech), Dougal Dobie (U Syd.) On behalf of the Global Relay of Observatories Watching Transients Happen (GROWTH) collaboration The DES-GW team conducted target-of-opportunity observations (NOAO PID 2019A-0235; PI Soares-Santos) of the localization region (GCN 25208; LALInference) of the gravitational wave trigger S190728q (GCN 25187) with the 4-m Victor M. Blanco telescope, equipped with the 3 square degree Dark Energy Camera. The data were made immediately public. We downloaded the data in real-time and processed them through a custom pipeline designed to search for optical counterparts to gravitational wave events in DECam images (Goldstein, Andreoni et al. 2019; Andreoni, Goldstein et al. 2019), using reference images from the DECam Legacy Survey DR7 (Dey et al. 2019). We applied standard filtering criteria including rejecting stellar sources and moving objects and applying machine learning algorithms (Goldstein et al. 2015). We report the discovery of the following objects, and to aid in prioritizing follow-up, we give the probability contour of the latest sky map (GCN 25208) that they lie within. +---------------------------------------------------------------------------------------------+ |Internal Name | RA (deg) | DEC (deg) | Filter | Mag | Magerr | TNS Name | Within | +--------------+-------------+-------------+--------+-------+---------+-----------+-----------+ |DG19rxclb | 314.455468 | +9.251135 | r | 21.5 | 0.35 | AT2019jvb | 50% reg. | |DG19blknb | 318.492802 | +14.786966 | r | 20.0 | 0.25 | AT2019lvt | 50% reg. | |DG19arsob | 313.646387 | +7.566747 | r | 22.0 | 0.25 | AT2019lvw | 50% reg. | |DG19tfmlb | 315.728720 | +12.515448 | r | 21.1 | 0.30 | AT2019lvv | 90% reg. | |DG19zrjmb | 311.437716 | +7.919455 | r | 20.6 | 0.30 | AT2019lvx | 90% reg. | |DG19jufnb | 317.097475 | +14.326338 | r | 20.6 | 0.20 | AT2019lvu | 50% reg. | |DG19bfhpb* | 316.494483 | +9.978795 | r | 21.0 | 0.30 | AT2019lvy | 90% reg. | +---------------------------------------------------------------------------------------------+ * Has previous detections in ZTF. We will continue to report additional candidates via TNS and GCN. Additional analysis and continued follow-up is in progress and encouraged. GROWTH is a worldwide collaboration comprising Caltech, USA; IPAC, USA, WIS, Israel; OKC, Sweden; JSI/UMd, USA; U Washington, USA; DESY, Germany; MOST, Taiwan; UW Milwaukee, USA; LANL USA; Tokyo Tech, Japan; IIT-B, India; IIA, India; LJMU, UK; TTU, USA; and USyd, Australia. ZTF acknowledges the generous support of the NSF under AST MSIP Grant No 1440341. GROWTH acknowledges generous support of the NSF under PIRE Grant No 1545949. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25216 SUBJECT: S190728q: MASTER multiple previous outbursts detection of ZTF19abjethn=AT2019lvs DATE: 19/07/29 10:28:42 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs V. Lipunov, E. Gorbovskoy, V.Kornilov, N.Tyurina, P.Balanutsa, A.Kuznetsov, F.Balakin, V.Vladimirov, D. Vlasenko, I.Gorbunov,D.Zimnukhov, V.Senik, A.Chasovnikov, D.Kuvshinov (Lomonosov Moscow State University, SAI, Physics Department), R. Podesta, C.Lopez, F. Podesta, C.Francile (Observatorio Astronomico Felix Aguilar OAFA), H.Levato (Instituto de Ciencias Astronomicas, de la Tierra y del Espacio ICATE), R. Rebolo, M. Serra (The Instituto de Astrofisica de Canarias) D. Buckley (South African Astronomical Observatory), O.A. Gres, N.M. Budnev, O.Ershova (Irkutsk State University, API), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), V. Yurkov, A. Gabovich, Yu. Sergienko (Blagoveschensk Educational State University) MASTER Global Robotic Net ( http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) observed S190728q (LIGO GCN 21187) since 2019-07-28 07:00:29 UT (Lipunov et al. GCN 25183). MASTER database has previous outbursts of Zwicky Transient Facility (ZTF) OT ZTF19abjethn=AT2019lvs (Kasliwal et al. GCN25199, R.A.,Dec=326.395431 +20.690590) since 2010, preliminary automatic MASTER unfiltered photometry is the following (W=0.2B+0.8R calibrated by USNO-B1 B2,R2 thousands field stars) Date,Time_UT m_OT MASTER-site 2010-10-26 17:41:20 18.5 MASTER-Kislovodsk 2012-11-05 16:38:30 18.4 MASTER-Kislovodsk 2014-10-27 16:49:43 18.6 MASTER-Kislovodsk 2016-06-08 01:53:30 19.2 MASTER-IAC This OT reobserved by MASTER-OAFA with unfiltered m_OT=15.4 (was also observed by Zwicky again Goldstein et al. GCN 25202, Zhou et al. GCN 25201, PanSTARRS Smartt et al. GCN 25204, LCO Ahumada et al. GCN 25206, WHT Magee et al. GCN 25209 - CV classification TShao Belkin et al. GCN 25212) The message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25217 SUBJECT: LIGO/VIRGO S190728q: No candidate counterparts from ATLAS observations DATE: 19/07/29 13:26:10 GMT FROM: Shubham Srivastav at QUB ​S. Srivastav, O. McBrien, K. W. Smith, D. R. Young, M. Dobson, S. J. Smartt, J. Gillanders, P. Clark, D. O'Neil, S. Sim (QUB), L. Denneau, H. Flewelling, A. Heinze, J. Tonry, H. Weiland (IfA, Univ. Hawaii), A. Rest (STScI), B. Stalder (LSST), C. Stubbs (Harvard) We report observations of the skymap for the BBH event S190728q (The LIGO Scientific Collaboration and the Virgo Collaboration, GCN 25187) with the ATLAS telescope system (Tonry et al. 2018, PASP, 13, 164505). ATLAS is a twin 0.5m telescope system on Haleakala and Mauna Loa employing two filters - cyan and orange. While carrying out the primary mission for Near Earth Objects, we can adjust the schedule rapidly to point at LVC gravitational wave skymaps. Sequences of 30 sec images were taken in the ATLAS c band, and at each pointing position a sequence of quads (4 x 30 sec) was taken. The images were processed with the ATLAS pipeline and reference images subtracted from each one. Transient candidates were run through our standard filtering procedures, combined with machine learning algorithms (e.g. Wright et al. 2015, MNRAS, 449, 451). Candidates were spatially cross-matched with known minor planets, and star, galaxy, AGN and multi-wavelength catalogues (as described in Smartt et al. 2016, MNRAS, 462 4094, Stalder et al. 2017, ApJ, 850, 149). We covered 99.04 square degrees of the 90% credible region (GCN 25208; LALInference), totalling 91.7% of the event’s localisation likelihood. Data acquisition began at MJD 58692.36 or 2019-07-28 08:39:33.29 (UTC), ~100 mins after the PRELIMINARY notice and ~114 mins after the GW merger event. We found no new transients to a magnitude of c < 19.8 (the median of the 5 sigma limits of the individual 30 sec images) between 114 to 261 minutes after the BBH merger within the LALInference skymap. This work has made use of data from the Asteroid Terrestrial-impact Last Alert System (ATLAS) project. ATLAS is primarily funded to search for near earth asteroids through NASA grants NN12AR55G, 80NSSC18K0284, and 80NSSC18K1575; byproducts of the NEO search include images and catalogs from the survey area. The ATLAS science products have been made possible through the contributions of the University of Hawaii Institute for Astronomy, the Queen's University Belfast, and the Space Telescope Science Institute. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25220 SUBJECT: LIGO/Virgo S190728q/IceCube neutrino candidate: No counterpart candidates in the Swift-XRT Observations DATE: 19/07/30 00:44:43 GMT FROM: Azadeh Keivani at Columbia U LIGO/Virgo S190728q/IceCube neutrino candidate: No counterpart candidates in the Swift-XRT Observations A. Tohuvavohu (PSU), A. Keivani (Columbia U.), J. A. Kennea (PSU), P. A. Evans (U. Leicester), S. Countryman (Columbia U.), Z. Marka (Columbia U.), S. Marka (Columbia U.), I. Bartos (U. Florida), D. B. Fox (PSU) The Neil Gehrels Swift Observatory observed the field of the IceCube track-like muon neutrino candidate (RA, Dec = 312.87d, 5.85d; GCN #25210) consistent with the sky localization of gravitational-wave candidate S190728q (GCN #25187) covering ~14.5 sq degrees in 145 tiles (tiling map at this url: https://tinyurl.com/y52pug65), to cover the most probable regions of the joint GW and neutrino localization (90%-containment radius: 4.8d). The observations start from 19:27 UT on July 28th and ended at 11:41 UT on July 29, 2019, and achieved an average depth of ~5 x 10^-12 erg s^-1 cm^-2 in soft X-rays (0.3-10 keV). Three X-ray sources were detected in these observations which all match known X-ray sources. None of these are above their cataloged flux values. Source, RA, Dec, XRT count rate (ct s^-1) ------------------------------------------------------------------------------------------------------------------ 1RXS J205242.6+081039, 313.1760, 8.1785, 0.11 (±0.04) ------------------------------------------------------------------------------------------------------------------ 1RXS J205421.7+090229, 313.58716, 9.0381, 0.06 (±0.03) ------------------------------------------------------------------------------------------------------------------ XMMSL2 J204928.9+060159, 312.37177, 6.0305, 0.11 (±0.04) //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25222 SUBJECT: LIGO/Virgo S190728q: GRAWITA VST-ESO PARANAL observations DATE: 19/07/30 14:05:35 GMT FROM: Aniello Grado at INAF-OAC AUTHORS: A. Grado (INAF-Napoli), E. Cappellaro (INAF-Padova), F. Getman (INAF-Napoli), S. Yang (INAF-Padova), E. Brocato (INAF-Abruzzo), P. D’Avanzo (INAF-BRERA), S. Covino (INAF-Brera), G. Greco (Universita' Urbino) on behalf of GRAWITA. We observed 45 sqdeg in two epochs covering the field of S170728q (LIGO/Virgo, S. Antier, GCN #25208) in r' band with the VLT Survey Telescope (VST) equipped with Omegacam (1 sqdeg FOV) (Proposal ID ESO 0103.D-0070 ). Observations of the first epoch started on 2019-07-29 at 03:14 UT and ended at 06:52. Observations of the second epoch started on 2019-07-30 at 03:01 end ended at 06:56 UT. The observations, covering 65% of the localization probability region, were organized in group of 3x3 deg, the coordinates of the center of each group are: RA(J2000) Dec(J2000) ------------------------ 319.55602 18.0797 317.09440 15.01752 315.45366 12.04954 313.95922 8.53513 313.16805 5.85237 Each 1 sqdeg pointing was observed three times for a total exposure time of 135 seconds.The average 50% completeness for point sources is 22.4 mag. Analysis of the images is in progress. We acknowledge excellent support from the ESO User Support Department and from ESO observing staff in Paranal. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25224 SUBJECT: LIGO/Virgo S190728q: Optical transients from Pan-STARRS coverage during first 2 nights DATE: 19/07/30 16:32:14 GMT FROM: Ken Smith at Queen's University Belfast M. Huber (IfA, Univ. of Hawaii), K. W. Smith (QUB), K. Chambers, A. Schulz (IfA), S. J. Smartt, D. R. Young, O. McBrien, J. Gillanders, S. Srivastav, D. O'Neil, P. Clark, S. Sim (QUB), T. de Boer, J. Bulger, J. Fairlamb, M. Huber, C.-C. Lin, T. Lowe, E. Magnier, R. J. Wainscoat, M. Willman (IfA, Univ. of Hawaii), T.-W, Chen (MPE), A. Rest (STScI), C. Stubbs (Harvard) We report observations of the LALInf skymap of the BBH event s190728q (The LIGO Scientific Collaboration and the Virgo Collaboration, GCN 25208, 25187) with the Pan-STARRS1 telescope (Chambers et al. 2016, arXiv:1612.05560C). Images were taken in the PS1 w and i-bands (Tonry et al. 2012, ApJ 750, 99). Beginning at 2019-07-28 10:08:31 UT (58692.4226) or 3.4hrs after the detection of S190728q, observations started in the w-band in the standard NEO search sequence. At each pointing position a sequence of quads (4 x 45 sec) was taken. This observing sequence ensures exactly the same pointing position for each of the quads. Observations of the map finished on 2019-07-28 14:44:53 UT. On the following night, beginning at 2019-07-29 08:51:02 a series of 45sec i-band dithered images were taken to cover the map. We finished observing at 2019-07-29 10:06:41. In total PS1 covered 105 squ. degrees of the LALInference.offline.fits,gz map of the 90% credible region and we estimate we covered a sky region totalling 92% of the event's localisation likelihood. The images were processed with the IPP (Magnier et al. 2016, arXiv:1612.05240) and difference images were produced using the Pan-STARRS1 Science Consortium 3Pi images as reference frames. Transient candidates were run through our standard filtering procedures, combined with a machine learning algorithm (Wright et al. 2015, MNRAS, 449, 451) were applied and all candidates were spatially cross-matched with known minor planets, and major star, galaxy, AGN and multi-wavelength catalogues (as described in Smartt et al. 2016, MNRAS, 462 4094). We report the following transients which are all within the 90% contour of the LALInference.offline.fits map. They are all supernova like candidates, either offset from a clear galaxy or no obvious host. The majority of these are detected over the 2 nights and do not show any fast fading or rising. The redshifts below are all photometric from SDSS DR15 or GLADE. For reference the redshift range corresponding to the luminosity distance of S190728q (GCN 25208) is approximately 0.14 < z < 0.22. Name TNS Name RA (J2000) Dec (J2000) Disc MJD Disc Mag photoz PS19dxk AT2019lzs 20 42 38.23 +06 05 53.6 58692.43 21.92 w PS19dxc AT2019lzb 20 45 55.34 +02 05 53.5 58692.43 20.62 w 0.464 PS19dxl AT2019lzr 20 47 08.30 +07 16 16.2 58692.43 21.37 w PS19dxb AT2019lzc 20 52 54.72 +02 31 43.6 58692.43 21.69 w 0.228 PS19dwv AT2019lyv 21 00 06.51 +12 16 54.5 58692.53 21.99 w 0.046 PS19dxo AT2019lzv 21 01 02.31 +14 23 48.5 58692.52 20.96 w PS19dxn AT2019lzt 21 01 13.26 +13 29 39.0 58692.53 21.05 w PS19dxf AT2019lzg 21 03 16.16 +14 22 50.9 58692.54 20.91 w PS19dxg AT2019lzf 21 11 56.20 +17 14 27.2 58692.58 21.80 w 0.713 PS19dwz AT2019lyz 21 14 09.78 +13 37 04.8 58692.53 21.58 w PS19dxm AT2019lzu 21 26 42.01 +17 17 25.8 58692.58 21.18 w PS19dxe AT2019lzd 21 29 51.15 +19 10 33.6 58692.58 22.10 w 0.090 PS19dxd AT2019lze 21 33 04.06 +21 25 19.2 58692.58 21.77 w The one exception is PS19dxf, which appears to show a fast rise and decline of 1 mag in 33 minutes in the w-band images of the first night. This is probably an M-dwarf flare, as it is coincident with an uncatalogued, red and faint source in both Pan-STARRS and DECaLs imaging surveys. In Pan-STARRS it is only detected in z. Star-galaxy distinction is not possible, but a galactic M-dwarf flare is the most likely explanation for this transient. Confirmation of DECam-GROWTH objects from Goldstein et al. (GCN 25215) or TNS registered: Name DG Name RA (J2000) Dec (J2000) Det. MJD Mag TNS Name PS19dwt DG19qukmb 20 44 56.55 +07 23 58.6 58692.43 20.57 w AT2019lyc PS19dwy DG19bfhpb 21 05 58.67 +09 58 43.7 58692.53 21.05 w AT2019lvy PS19dxp DG19tneob 21 15 01.04 +14 59 22.7 58692.58 20.37 w AT2019lxc Other known objects we recovered but were previously discovered by Pan-STARRS or ZTF: Name RA (J2000) Dec (J2000) Det. MJD Mag TNS Name PS19dwm 21 34 22.65 +21 20 30.6 58692.58 20.66 w AT2019lxm ZTF19aavndxo 20 47 51.02 +10 17 35.5 58693.38 19.48 i AT2019fyt PS19dxj 21 31 22.91 +20 34 04.4 58692.58 20.95 w AT2019lzo We also note that DG19rxclb as reported in Goldstein et al. (GCN 25215) is an old object (AT2019jvb) discovered by PS1 and registered on TNS on 2019-06-01. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25226 SUBJECT: LIGO/Virgo S190728q: MITSuME Okayama and Bisei Follow-Up of ZTF19abjethn (AT2019lvs) DATE: 19/07/31 02:16:30 GMT FROM: Katsuhiro L. Murata at Nagoya U Y. Yatsu, N. Kawai, K. L. Murata, R. Adachi, K. Iida, M. Oeda, K. Shiraishi, M. Niwano, F. Ogawa, S. Toma and R. Hosokawa (Tokyo Tech), R. Itoh (Bisei Astronomical Observatory) report on behalf of the MITSuME collaboration: We observed the ZTF optical transient ZTF19abjethn (AT2019lvs) listed in Kasliwal et al. (GCN 25199) using the optical three color (g’, Rc, and Ic) CCD cameras attached to the MITSuME 50 cm telescope of Okayama Astrophysical Observatory, and using the CCD camera with V, R, and I band filters attached to the 101cm telescope of Bisei Astronomical Observatory. The observation of the MITSuME and the Bisei telescopes started on 2019-07-28 13:29:47 UT and 2019-07-28 15:27:39 UT, respectively. The measured magnitudes are listed as follows. | telescope | MID-UT | T-EXP [sec] | magnitudes | ----------------------------------------------------------------------------------------------- | MITSuME Okayama 50cm | 15:09:47 | 10260 | g’ = 17.40 +/- 0.07 Rc = 17.70 +/- 0.06 Ic = 17.53 +/- 0.06 | | Bisei 101 cm | 15:55:09 | 600 | V = 17.23 +/- 0.02 | | Bisei 101 cm | 15:37:27 | 1200 | R = 17.41 +/- 0.02 | | Bisei 101 cm | 16:08:21 | 600 | I = 17.40 +/- 0.04 | --------------------------------------------------------------------------------------------------- T-EXP: Total Exposure time We used PS1 catalog for flux calibration. The magnitudes are expressed in the AB system. The color terms are not used in the above magnitudes. There are non-negligible differences in the magnitudes between MITSuME and Bisei, which might be explained by their color-terms. This observation was carried out by the Global Relay of Observatories Watching Transients Happen (GROWTH) collaboration. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25235 SUBJECT: LIGO/Virgo S190728q: ZTF Forced Photometry for PS1 and DECam-GROWTH optical candidates, and a note on DECam Photometry from GCN 25215 DATE: 19/07/31 18:43:12 GMT FROM: Igor Andreoni at Caltech Igor Andreoni (Caltech), Erik Kool (OKC), Danny Goldstein (Caltech), Frank Masci (IPAC), Mansi Kasliwal (Caltech), Matthew Graham (Caltech) On behalf of the Zwicky Transient Facility (ZTF) and Global Relay of Observatories Watching Transients Happen (GROWTH) collaborations We performed forced photometry on images acquired with the Zwicky Transient Facility (ZTF; Bellm et al. 2019, Graham et al. 2019) for the the optical transients reported so far by the Pan-STARRS (PS1; Huber et al., GCN #25224) and DECam-GROWTH (Goldstein et al., GCN #25215) teams. Forced photometry was performed on images processed through the ZTF reduction and image subtraction pipelines at IPAC (Masci et al. 2019). The following table includes candidates with no detections before the trigger time of S190728q (2019-07-28 06:45:10.529 UT, GCN #25187). For these sources, we report the latest relevant upper limits or confirmation detections. An association between these candidates and S190728q cannot be excluded with our ZTF observations. +----------------------------------------------------+ | Name | TNS name | Date (UT) | ZTF phot | +----------------------------------------------------+ |PS19dxc | AT2019lzb | 2019-07-06 09:03 | r > 21.8 | | | | 2019-07-28 10:51 | r > 21.8 | +----------------------------------------------------+ |PS19dxb | AT2019lzc | 2019-07-21 07:03 | i > 20.3 | +----------------------------------------------------+ |PS19dxn | AT2019lzt | 2019-07-26 09:20 | r > 21.5 | | | | 2019-07-28 10:31 | r = 21.0 | | | | 2019-07-30 08:41 | r > 21.7 | +----------------------------------------------------+ |PS19dxf | AT2019lzg | 2019-07-26 09:20 | r > 21.5 | | | | 2019-07-30 08:42 | r > 21.6 | +----------------------------------------------------+ |PS19dxg | AT2019lzf | 2019-01-10 02:24 | r > 18.8 | | | | 2019-07-28 10:46 | r = 22.1 | | | | 2019-07-29 04:08 | r > 20.5 | +----------------------------------------------------+ |PS19dwz | AT2019lyz | 2019-07-05 11:26 | g > 21.3 | +----------------------------------------------------+ |PS19dxm | AT2019lzu | 2019-07-14 11:05 | r = 21.5 | +----------------------------------------------------+ |PS19dxd | AT2019lze | 2019-07-24 09:33 | r > 21.3 | | | | 2019-07-28 08:04 | r = 21.6 | | | | 2019-07-31 08:07 | r = 21.5 | +----------------------------------------------------+ |DG19arsob | AT2019lvw | 2019-01-07 02:20 | r > 18.6 | | | | 2019-07-28 10:42 | r = 22.1 | | | | 2019-07-29 04:34 | r > 20.0 | +----------------------------------------------------+ |DG19tfmlb | AT2019lvv | 2019-07-26 09:20 | r > 21.5 | | | | 2019-07-30 08:42 | r > 21.6 | +----------------------------------------------------+ |DG19zrjmb | AT2019lvx | 2019-07-06 07:31 | r = 21.5 | +----------------------------------------------------+ We note that PS19dxn / AT2019lzt may be evolving rapidly. The candidate is detected by both PS1 and ZTF hours after S190728q (ZTF detection on 2019-07-28 10:31 UT, PS1 detection on 2019-07-28 12:43 UT) and it is not detected by ZTF on the following days. The following table includes candidates with ZTF pre-detections. For these candidates, an association with S190728q can be ruled out: +----------------------------------------------------+ | Name | TNS name | Date (UT) | ZTF phot | +----------------------------------------------------+ |PS19dxk | AT2019lzs | 2019-07-06 07:31 | r = 20.9 | |PS19dxl | AT2019lzr | 2019-07-06 07:32 | r = 21.2 | |PS19dwv | AT2019lyv | 2019-07-08 08:51 | r = 21.7 | |PS19dxo | AT2019lzv | 2019-07-08 08:32 | r = 20.9 | |PS19dxe | AT2019lzd | 2019-07-13 07:06 | r = 20.4 | |DG19jufnb | AT2019lvu | 2019-07-06 09:38 | i = 20.7 | +----------------------------------------------------+ Other candidates were reported during the follow-up of S190827q, but their association with the gravitational wave event has already been ruled out by photometric pre-detection or by spectroscopic classification. In particular, those include DG19rxclb (GCN #25215, GCN #25224), DG19blknb (GCN #25215 GCN #25221), and DG19bfhpb (GCN #25215). We caution that we plan to shortly revise the DECam photometry in GCN #25215 as it was impacted by the poor quality of some of the available reference imaging from the DECam Legacy Survey DR7. We thank Stephen Smartt for useful discussions. The ZTF forced-photometry service was funded under the Heising-Simons Foundation grant #12540303 (PI: Graham). ZTF and GROWTH are worldwide collaborations comprising Caltech, USA; IPAC, USA, WIS, Israel; OKC, Sweden; JSI/UMd, USA; U Washington, USA; DESY, Germany; MOST, Taiwan; UW Milwaukee, USA; LANL USA; Tokyo Tech, Japan; IIT-B, India; IIA, India; LJMU, UK and USyd, Australia. ZTF acknowledges the generous support of the NSF under AST MSIP Grant No 1440341. GROWTH acknowledges generous support of the NSF under PIRE Grant No 1545949. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25236 SUBJECT: LIGO/Virgo S190728q: Correction to GCN #25235: also PS19dxm and DG19zrjmb are not associated with S190728q DATE: 19/07/31 19:17:39 GMT FROM: Igor Andreoni at Caltech Igor Andreoni (Caltech), Danny Goldstein (Caltech), Erik Kool (OKC) This GCN is a correction of GCN #25235, presenting ZTF photometry of Pan-STARRS and DECam-GROWTH candidates (GCN #25224, GCN #25215). In GCN #25235, the following candidates were included in the table of transients with no ZTF detection before S190718q (GCN #25187). Instead, they should have been included in the table of candidates with ZTF pre-detections. +----------------------------------------------------+ | Name | TNS name | Date (UT) | ZTF phot | +----------------------------------------------------+ |PS19dxm | AT2019lzu | 2019-07-14 11:05 | r = 21.5 | +----------------------------------------------------+ |DG19zrjmb | AT2019lvx | 2019-07-06 07:31 | r = 21.5 | +----------------------------------------------------+ Hence we exclude the association of PS19dxm / AT2019lzu and DG19zrjmb / AT2019lvx with S190728q. Apologies for any confusion that this could have caused. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25237 SUBJECT: LIGO/Virgo S190728q: No counterpart candidates in H.E.S.S. observations DATE: 19/07/31 20:28:00 GMT FROM: Fabian Schussler at CEA 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 S190728q (GCN #25187) using the LALInference map (GCN #25208). Observations started July 28 at 20:17 UTC and lasted until July 29 02:45 UTC. A total of 7 pointings allowed to cover about 80% of the LALInference map provided in the Update-5 GCN notice and the GCN circular #25208. Observations of each of the pointings reached at least a 5-sigma sensitivity of about 20% of the flux from the Crab nebula. A preliminary analysis did not reveal significant gamma-ray emission in any of the observed fields. Further analyses of the data are on-going. The following regions-of-interests were covered. Given is the start time of the first observation of each of the pointings and the center of the ROI. Time (UTC) RA (J2000) Dec (J2000) 2019-07-28 20:17 20h51m13s 7d01m49s 2019-07-28 21:12 20h52m22s 8d09m36s 2019-07-28 22:17 21h08m26s 15d01m03s 2019-07-28 22:59 20h57m32s 10d48m25s 2019-07-28 23:47 20h51m55s 5d40m45s 2019-07-29 00:16 21h14m46s 17d11m31s 2019-07-29 01:03 21h04m34s 12d56m30s 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, France, Germany, Ireland, Japan, the Netherlands, Poland, South Africa, Sweden, UK, and the host country, Namibia. For more details see https://www.mpi-hd.mpg.de/hfm/HESS/ //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25253 SUBJECT: LIGO/Virgo S190728q: AT2019lzt 10.4m GTC spectroscopy DATE: 19/08/02 08:04:43 GMT FROM: Alberto J. Castro-Tirado at IAA-CSIC A. J. Castro-Tirado (IAA-CSIC), A. F. Valeev and V. V. Sokolov (SAO-RAS), Y.-D. Hu and E. Fernandez-Garcia (IAA-CSIC), I. Carrasco and A. Castellon (UMA), P. Zarco-Villegas (SMA), X.-Y. Li (NIAOT) and P. Pessev (GRANTECAN, IAC, ULL), on behalf of a larger collaboration, report: Following the detection of AT2019lzt (Andreoni et al., GCNC 24235) within the error area of the GW event S190728q (LVC, GCNC 25187), we obtained imaging and optical spectra (1200s) covering the range 3700-7500 A with the 10.4m GTC telescope equipped with OSIRIS in La Palma (Spain) starting on Aug 2, 04:15 UT. AT2019lzt magnitude on Aug 2, 03:50 UT was measured to be r = 21.13 +/- 0.02. The AT2019lzt spectrum (broad lines) is consistent with a SN Ia at 4 days post maximum at the nearby host galaxy redshift (z = 0.193 +/- 0.001, based on the narrow emission lines from the galaxy). Therefore AT2019lzt is unrelated to the GW event S190728q. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25261 SUBJECT: LIGO/Virgo S190728q: AT2019lzc 10.4m GTC spectroscopy DATE: 19/08/04 09:00:46 GMT FROM: Alberto J. Castro-Tirado at IAA-CSIC A. F. Valeev (SAO-RAS), A. J. Castro-Tirado, Y.-D. Hu and E. Fernandez-Garcia (IAA-CSIC), V. V. Sokolov (SAO-RAS), I. Carrasco and A. Castellon (UMA) and N. Castro-Rodriguez (GRANTECAN, IAC, ULL), on behalf of a larger collaboration, report: Following the detection of AT2019lzc (Huber et al., GCN 25224, Andreoni et al., GCNC 24235) within the error area of the GW event S190728q (LVC, GCNC 25187), we obtained imaging and optical spectra covering the range 3700-7500 A with the 10.4m GTC telescope equipped with OSIRIS in La Palma (Spain) starting on Aug 4, 04:30 UT. AT2019lzc magnitude on Aug 4, 04:30 UT was measured to be r = 20.9 +/- 0.1. The AT2019lzc 1200s spectrum displays broad lines and is consistent with a SN Ia at about 20 days post maximum at the nearby host galaxy redshift (z = 0.207 +/- 0.005, based on the narrow emission lines from the galaxy). Therefore AT2019lzc is unrelated to the GW event S190728q. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25276 SUBJECT: LIGO/Virgo S190728q: AT2019lvw 10.4m GTC spectroscopy DATE: 19/08/05 19:03:01 GMT FROM: Alberto J. Castro-Tirado at IAA-CSIC Y.-D. Hu (IAA-CSIC), A. F. Valeev and V.V. Sokolov (SAO-RAS), A. J. Castro-Tirado and E. Fernandez-Garcia (IAA-CSIC), I. Carrasco and A. Castellon (UMA) and N. Castro-Rodriguez (GRANTECAN, IAC, ULL), on behalf of a larger collaboration, report: Following the detection of AT2019lvw (Goldstein et al., GCN 25215, Andreoni et al., GCNC 24235) within the error area of the GW event S190728q (LVC, GCNC 25187), we obtained imaging and optical spectra covering the range 3700-7500 A with the 10.4m GTC telescope equipped with OSIRIS in La Palma (Spain) starting on Aug 5, 04:00 UT. AT2019lvw magnitude on Aug 5, 04:30 UT was measured to be r = 22.15 +/- 0.05. The AT2019lvw 1200s spectrum displays broad lines and is consistent with a SN Ia at three-four weeks post maximum at the nearby host galaxy redshift (z = 0.270 +/- 0.001, based on the narrow emission lines from the galaxy). Therefore AT2019lvw is unrelated to the GW event S190728q. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25302 SUBJECT: LIGO/Virgo S190728q: New optical candidates from the DESGW program DATE: 19/08/09 05:17:38 GMT FROM: M. Soares-Santos at Fermi Lab Marcelle Soares-Santos (Brandeis U), Kenneth Herner (Fermilab), Alyssa Garcia (Brandeis U), Antonella Palmese (Fermilab), Robert Morgan (U. of Wisconsin-Madison), Nora Sherman (Fermilab), Tristan Bachmann (U Chicago), James Annis (Fermilab) On behalf of the DESGW collaboration* We report five new candidate counterparts to the LIGO/Virgo binary black hole merger S190728q (LVC, GCN No. 25187) found by our target of opportunity program, and provide additional photometry on one candidate discovered by GROWTH (PIs: Andreoni & Goldstein, GCN No. 25215). DESGW observed 108 square degrees, covering 81% of the LALInference localization probability (LVC, CGN No. 25208) to 23rd r-band magnitude in five epochs distributed within one week from the time of merger: EPOCH DELTA_MJD NIGHT 1 1.254 20190728 2 1.307 20190728 3 2.193 20190729 4 5.419 20190801 5 7.411 20190803 Images were processed by our difference imaging pipeline (Herner et al. 2017; see also Soares-Santos et al. 2015, 2017; Doctor et al. 2018; Morgan et al. 2019 for recent applications) using publicly available DECam images as templates. We employ a machine learning code (autoscan, Goldstein et al. 2015) to reject subtraction artifacts. Candidates were initially selected by requiring at least two high signal to noise detections on any two nights, rejecting asteroids. We then applied catalog-based vetting to reject variable stars, variable AGNs, and candidates with hosts at redshifts inconsistent with the distance reported by the LVC for S190728q (874 +/- 171 Mpc). Those catalogs included Gaia DR2, SDSS DR15, and DECaLS DR8. The final vetting was done via visual inspection. We matched our remaining candidates using the Transient Name Server to avoid reporting those previously reported by other groups. In our final sample, we find 5 new candidates that show a significant (2 sigma) decrease in flux. This requirement is motivated by the fact that our primary contaminant, supernovae, typically vary in timescales that are much longer than one week. The five candidates that meet all of our criteria are: NAME TNS_NAME RA DEC DISCOVERY_MJD DISCOVERY_MAG LASTOBS_MJD LASTOBS_MAG desgw-190728a 2019myj 316.871395 13.250478 58693.129 22.41 58699.286 22.65 desgw-190728b 2019myf 318.831885 17.605576 58693.152 21.83 58699.309 22.00 desgw-190728c 2019myg 314.8038 8.559899 58693.146 22.77 58699.303 22.66 desgw-190728d 2019myh 317.40364 12.125172 58693.149 22.29 58699.306 22.64 desgw-190728e 2019myi 316.382118 12.397139 58693.149 21.91 58699.306 22.17 We also checked for increasing flux at the same significance level and found no additional candidates. The host galaxy redshift is available for desgw-190728b and is marginally consistent with the LVC estimate of distance to the merger. Candidate desgw-190728e has a clear host without redshift information. The other three candidates appear to be hostless. CANDIDATE_ID HOST_ID HOST_MAG HOST_Z HOST_ZERR desgw-190728b SDSS J211519.63+173623.6 18.65 0.1147 0.0253 desgw-190728e 2MASX J21053105+1221566 18.22 -- -- We did detect all of the nine candidates previously reported by GROWTH (Goldstein et al., GCN 25215). Two of them met our selection criteria: 2019lvy and 2019lvu. The former we exclude due to a pre-merger detection in ZTF. We provide additional photometry for their remaining candidate: NAME TNS_NAME RA DEC DISCOVERY_MJD DISCOVERY_MAG LASTOBS_MJD LASTOBS_MAG 2019lvu DG19jufnb 317.097475 14.326338 58693.129 20.84 58699.288 21.78 All magnitudes reported are observed magnitudes. We encourage spectroscopic followup of these candidates. Data processing of images from all five epochs has concluded and a detailed analysis is ongoing. We expect to report updates soon. The DECam Search & Discovery Program for Optical Signatures of Gravitational Wave Events (DESGW) is carried out by the Dark Energy Survey (DES) collaboration in partnership with wide ranging groups in the community. DESGW uses data obtained with the Dark Energy Camera (DECam), which was constructed by the DES collaboration with support from the Department of Energy and member institutions, and utilizes data as distributed by the Science Data Archive at NOAO. NOAO is operated by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation. *DESGW collaboration: Sahar Allam (Fermilab), James Annis (Fermilab), Iair Arcavi (Tel Aviv University), Tristan Bachmann (U Chicago), Paulo Barchi (INPE/Brazil), Thomas Beatty (U of Arizona) Keith Bechtol (U of Wisconsin-Madison), Federico Berlfein (Brandeis U), Antonio Bernardo (IAG-USP/Brazil), Dillon Brout (University of Pennsylvania), Robert Butler (Indiana University), Melissa Butner, (Fermilab), Annalisa Calamida (STScI), Hsin-Yu Chen (Harvard U), Chris Conselice (University of Nottingham), Carlos Contreras (STScI), Jeff Cooke (Swinburne University), Chris D’Andrea (University of Pennsylvania), Tamara Davis (UQ/Australia), Reinaldo de Carvalho (NAT - Universidade Cruzeiro do Sul/Universidade Cidade de Sao Paulo), H. Thomas Diehl (Fermilab), Zoheyr Doctor (U Chicago), Alex Drlica-Wagner (Fermilab), Maria Drout (U Toronto), Maya Fishbach (U Chicago), Francisco Forster (U de Chile/Chile), Ryan Foley (UCSC), Joshua Frieman (Fermilab & University of Chicago), Chris Frohmaier (University of Portsmouth), Ori Fox (STScI), Alyssa Garcia (Brandeis University), Juan Garcia-Bellido (Universidad Autonoma de Madrid), Mandeep Gill (SLAC/Stanford U), Robert Gruendl (NCSA), Will Hartley (University College London), Kenneth Herner (Fermilab), Daniel Holz (U Chicago), Jorge Horvath (IAG-USP/Brazil), D. Andrew Howell (Las Cumbres Observatory), Richard Kessler (University of Chicago), Charles Kilpatrick (UCSC), Nikolay Kuropatkin (Fermilab), Ofer Lahav (University College London), Huan Lin (Fermilab), Andrew Lundgren (Portsmouth), Martin Makler (CBPF/Brazil), Clara Martinez-Vazquez (CTIO/NOAO), Curtis McCully (Las Cumbres Observatory), Mitch McNanna (U of Wisconsin-Madison), Robert Morgan (U of Wisconsin-Madison), Gautham Narayan (STScI), Eric Neilsen (Fermilab), Robert Nichol (University of Portsmouth), Antonella Palmese (Fermilab), Francisco Paz-Chinchon (NCSA & UIUC), Matthew Penny (OSU), Maria Pereira (Brandeis University), Sandro Rembold (UFSM/Brazil), Armin Rest (STScI & JHU), Livia Rocha (IAG-USP/Brazil), Russell Ryan (STScI), Masao Sako (University of Pennsylvania), Samir Salim (Indiana University), David Sand (U of Arizona), Daniel Scolnic (Duke University), Nora Sherman (Fermilab), J. Allyn Smith (Austin Peay State University), Mathew Smith (University of Southampton), Marcelle Soares-Santos (Brandeis U), Lou Strolger (STScI), Riccardo Sturani (UFRN/Brazil), Mark Sullivan (University of Southampton), Masaomi Tanaka (NAOJ/Japan), Nozomu Tominaga (Konan U/Japan), Douglas Tucker (Fermilab), Yousuke Utsumi (Stanford U), Stefano Valenti (UC Davis), Kathy Vivas (NOAO/CTIO), Alistair Walker (NOAO/CTIO), Sara Webb (Swinburne University), Matt Wiesner (Benedictine University), Brian Yanny (Fermilab), Michitoshi Yoshida (NAOJ/Japan), Alfredo Zenteno (NOAO/CTIO), Luidhy Santana-Silva (Valongo Observatory), and the Dark Energy Survey (DES) Collaboration.