//////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25811 SUBJECT: LIGO/Virgo S190923y: Upper limits from IceCube neutrino searches DATE: 19/09/23 13:39:22 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 S190923y in a time range of 1000 seconds [3] centered on the alert event time (2019-09-23 12:47:39.646 UTC to 2019-09-23 13:04:19.646 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 S190923y calculated from the map circulated in the 2-Initial 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 S190923y ranges from 0.029 to 1.120 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: 25812 SUBJECT: LIGO/Virgo S190923y: Global MASTER-Net observations report DATE: 19/09/23 13:43:07 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-Tunka robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Applied Physics Institute, Irkutsk State University) started inspect of the LIGO/Virgo S190923y errorbox 374 sec after notice time and 798 sec after trigger time at 2019-09-23 13:09:17 UT, with upper limit up to 18.5 mag. The observations began at zenit distance = 75 deg. The sun altitude is -19.7 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=10825 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 889 | 2019-09-23 13:09:17 | MASTER-Tunka | (10h 15m 27.073s , +50d 15m 33.84s) | C | 180 | 18.5 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25813 SUBJECT: LIGO/Virgo S190923y: No counterpart candidates in HAWC observations DATE: 19/09/23 13:45:47 GMT FROM: Antonio Galvan at Inst.de Astronomia,UNAM The HAWC Collaboration (https://www.hawc-observatory.org) reports: The HAWC Collaboration performed a follow-up of the gravitational wave trigger S190923y. At the time of the trigger the HAWC local zenith was oriented towards (RA, Dec) = (98.5deg, 19.0deg). 52% 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 0.0deg to 45.0deg 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-06 erg/cm^2 to 1.1e-04 erg/cm^2 (6.4e-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: 25814 SUBJECT: LIGO/Virgo S190923y: Identification of a GW compact binary merger candidate DATE: 19/09/23 13:58:06 GMT FROM: Olivier Minazzoli at LIGO Virgo Collaboration The LIGO Scientific Collaboration and the Virgo Collaboration report: We identified the compact binary merger candidate S190923y during real-time processing of data from LIGO Hanford Observatory (H1) and LIGO Livingston Observatory (L1) at 2019-09-23 12:55:59.646 UTC (GPS time: 1253278577.646). The candidate was found by the PyCBC Live [1], MBTAOnline [2], and GstLAL [3] analysis pipelines. S190923y is an event of interest because its false alarm rate, as estimated by the online analysis, is 4.8e-08 Hz, or about one in 7 months. The event's properties can be found at this URL: https://gracedb.ligo.org/superevents/S190923y The classification of the GW signal, in order of descending probability, is NSBH (68%), Terrestrial (32%), BNS (<1%), BBH (<1%), or MassGap (<1%). Assuming the candidate is astrophysical in origin, there is strong evidence for the lighter compact object having a mass < 3 solar masses (HasNS: >99%). 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 [4], distributed via GCN notice about 6 minutes after the candidate For the bayestar.fits.gz sky map, the 90% credible region is 2107 deg2. Marginalized over the whole sky, the a posteriori luminosity distance estimate is 438 +/- 133 Mpc (a posteriori mean +/- standard deviation). The Virgo (V1) detector was not in observing mode at the time of the candidate but was collecting low-noise data during a tuning of the interferometer working point. We are investigating whether the V1 data can be used in parameter estimation analyses. For further information about analysis methodology and the contents of this alert, refer to the LIGO/Virgo Public Alerts User Guide < https://emfollow.docs.ligo.org/userguide/>. [1] Nitz et al. PRD 98, 024050 (2018) [2] Adams et al. CQG 33, 175012 (2016) [3] Messick et al. PRD 95, 042001 (2017) [4] Singer & Price PRD 93, 024013 (2016) //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25815 SUBJECT: LIGO/Virgo S190923y: No counterpart candidates in INTEGRAL SPI-ACS prompt observation DATE: 19/09/23 14:15:19 GMT FROM: Francesca Onori at INAF/IAPS Francesca Onori, Antonio Martin-Carrillo 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 S190923y (GCN 25814). At the time of the event (2019-09-23 12:55:59 UTC, hereafter T0), INTEGRAL was operating in nominal mode. The peak of the event localization probability was at an angle of 157 deg with respect to the spacecraft pointing axis. This orientation implies strongly suppressed (3% of optimal) response of ISGRI, somewhat suppressed (62% of optimal) response of IBIS/Veto, and somewhat suppresse d (43% of optimal) response of SPI-ACS. The background within +/-300 seconds around the event was very stable (excess variance 1.1). We have performed a search for any impulsive events in INTEGRAL SPI- ACS (as described in [2]) data. We do not detect any significant counterparts and estimate a 3-sigma upper limit on the 75-2000 keV fluence of 3.4e-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 ~3.4e-07 (6.7e-08) erg/cm^2/s at 1 s (8 s) time scale in 75-2000 keV energy range. For the mean reported distance 438.0 Mpc this corresponds to the limit on the tot al isotropic equivalent energy in 1 s of 7.9e+48 erg for the short GRB spectrum and for a long GRB spectrum isotropic equivalent luminosity in 1 s (8 s) of 4e+48 erg/s (1.5e+48 erg/s) We report for completeness and in order of FAP, all excesses identified in the search region. We find: 6 likely background excesses: scale | T | S/N | luminosity ( x 1e+49 erg/s) | FAP 1.7 | -41.9 | 4.4 | 8.61 +/- 2.55 +/- 5.68 | 0.0534 1.6 | -60.1 | 4.1 | 8.38 +/- 2.63 +/- 5.53 | 0.109 2.55 | 131 | 3.4 | 5.54 +/- 2.08 +/- 3.66 | 0.424 1 | 92 | 3.7 | 9.32 +/- 3.32 +/- 6.15 | 0.456 3.75 | -93.8 | 3 | 3.9 +/- 1.71 +/- 2.58 | 0.581 0.05 | -2.35 | 3.2 | 3.73 +/- 1.51 +/- 2.46 | 0.635 Note that FAP estimates (especially at timescales above 2s) may be possibly further affected by enhanced non-stationary local background noise. This list excludes any excesses for which FAP is close to unity. Part of the probability region was serendipitously observed by INTEGRAL FoV instruments (IBIS, JEM-X), analysis is ongoing. There was not ISGRI / IBIS detection at the time of the event, indicating absence of strong counterpart in IBIS. 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 -- Dr. Francesca Onori Postdoctoral Researcher IAPS, via Fosso del Cavaliere, 100, 00133 - Rome, Italy e-mail: francesca.onori@inaf.it Tel: +39 06 45488128 //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25816 SUBJECT: LIGO/Virgo S190923y : no neutrino counterpart candidate in ANTARES search DATE: 19/09/23 14:23:13 GMT FROM: Thierry Pradier at ANTARES/IPHC/U of Strasbourg 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 S190923y event using the 90% contour of the Initial bayestar probability map provided by the GW interferometers (GCN#25814 ). 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/S190923y_Initial.png . Considering the location probability provided by the LIGO/Virgo collaborations, there is a 41.7% 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 2019-09-23 12:55:59 and in the 90% contour of the S190923y event. The expected number of atmospheric background events in the region visible by ANTARES is 6.99e-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 5.03e-03 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: 25817 SUBJECT: LIGO/Virgo S190923y: Coverage and upper limits from MAXI/GSC observations DATE: 19/09/23 14:55:00 GMT FROM: Hitoshi Negoro at Nihon U H. Negoro (Nihon U.), S. Sugita, M. Serino (AGU), N. Kawai (Tokyo Tech), 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), M. Sugizaki (NAOC) report on behalf of the MAXI team: We examined MAXI/GSC all-sky X-ray images (2-20 keV) after the LVC trigger S190923y at 2019-09-23 12:55:59.645 UTC (GCN 25814). At the trigger time of S190923y, the high-voltage of MAXI/GSC was on. The instantaneous field of view of GSC at the GW trigger time covered 3% of the 90% credible region of the bayestar sky map, in which we found no significant new X-ray source. The first one-orbit (92 min) scan observation with GSC after the event covered 90% of the 90% credible region of the bayestar skymap from 12:55:59 to 14:27:58 UTC (T0+0 to T0+5519 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: 25819 SUBJECT: LIGO/Virgo S190923y: No counterpart candidates in AGILE-MCAL observations DATE: 19/09/23 15:05:54 GMT FROM: Claudio Casentini at INAF-IAPS C. Casentini (INAF/IAPS), F. Verrecchia (SSDC, and INAF/OAR), M. Tavani (INAF/IAPS, University of Rome Tor Vergata), M. Cardillo, G. Piano, A. Ursi (INAF/IAPS), F. Lucarelli, C. Pittori (SSDC, and INAF/OAR), A. Bulgarelli, V. Fioretti, N. Parmiggiani (INAF/OAS-Bologna), M. Pilia (INAF/OA-Cagliari), F. Longo (Univ. Trieste, and INFN Trieste), report on behalf of the AGILE Team: In response to the LIGO/Virgo GW event S190923y at T0 = 2019-09-23 12:55:59.646 (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 60% of the S190923y 90% c.l. localization region (LR) 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 S190923y LR, from a minimum of 1.08E-06 erg cm^-2 to a maximum of 7.70E-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: 25821 SUBJECT: LIGO/Virgo S190923y: Upper limits from AGILE-GRID observations DATE: 19/09/23 15:47:50 GMT FROM: Francesco Verrecchia at ASDC F. Verrecchia (SSDC, and INAF/OAR), C. Casentini (INAF/IAPS), M. Tavani (INAF/IAPS, and Univ.Roma Tor Vergata), M. Cardillo, G. Piano, A. Ursi (INAF/IAPS), F. Lucarelli, C. Pittori (SSDC, and INAF/OAR), A. Bulgarelli, V. Fioretti, N. Parmiggiani (INAF/OAS-Bologna), M. Pilia (INAF/OA-Cagliari), F. Longo (Univ. Trieste, and INFN Trieste) report on behalf of the AGILE Team: In response to the LIGO-Virgo GW event S190923y at T0 = 2019-09-23 12:55:59.646 UTC a preliminary analysis of the AGILE exposure at T0 shows that the Gamma-Ray Imaging Detector (GRID) exposure covered the 10% of the 90% c.l. localization region (LR) (40% of 90% c.l. localization region (LR) is occulted by Earth) at an off-axis angle of about 5 degrees. We performed an analysis of the GRID data in the energy range 50 MeV - 10 GeV on T0, where good exposure of the S190923y 90% c.l. LR was available. No candidate gamma-ray transient was detected. The following preliminary GRID values of 3-sigma upper limit (UL) are obtained: - from 7.0e-07 to 9.3e-07 erg cm^-2 s^-1, with exposure of about 10% of the LR over the time interval ( T0 - 2s ; T0 + 2s ); - from 2.9e-07 to 4.2e-07 erg cm^-2 s^-1, with exposure of about 10% of the LR over the time interval ( T0 ; T0 + 10s ); - from 6.5e-08 to 6.6e-06 erg cm^-2 s^-1, with exposure of about 11% of the LR over the time interval ( T0 ; T0 + 100s ) ; A map in Galactic coordinates showing the AGILE FoV at T0 is available at the site: https://tools.ssdc.asi.it/ImgView/Agile/AGILE_FOV_LIGO-VirgoS190923y_1909232521 These measurements were obtained with AGILE observing a large portion of the sky in spinning mode. Additional analysis of AGILE data is in progress. ========================================================================== Francesco Verrecchia ASDC - ASI Science Data Center - INAF/OAR - Istituto Nazionale di Astrofisica/ Osservatorio Astronomico di Roma - c/o ASI - Agenzia Spaziale Italiana - via del Politecnico snc, I-00133, Roma - Italy ========================================================================== e-mail:francesco.verrecchia@ssdc.asi.it phone:+39 068567 882 e-mail OAR:francesco.verrecchia@oa-roma.inaf.it ========================================================================== //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25823 SUBJECT: LIGO/Virgo S190923y: Upper limits from Fermi-GBM Observations DATE: 19/09/23 19:16:28 GMT FROM: Bagrat Mailyan at UAH B. Mailyan (UAH) and J. Wood (NASA) report on behalf of the Fermi-GBM Team and the GBM-LIGO/Virgo group For S190923y and using the initial bayestar skymap, Fermi-GBM was observing 42.3% of the localization probability at event time. There was no Fermi-GBM onboard trigger around the event time of the LIGO/Virgo detection of GW trigger S190923y (GCN 25814). 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. 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: 2.2 4.1 8.8 1.024 s: 0.74 1.3 2.4 8.192 s: 0.26 0.4 0.79 Assuming the median luminosity distance of 438 Mpc from the GW detection, we estimate the following intrinsic luminosity upper limits over the 1 keV-10 MeV energy range (in units of 10^48 erg/s): Timescale Soft Normal Hard ------------------------------------ 0.128s: 9.4 16.2 57.4 1.024s: 3.2 5.1 15.6 8.192s: 1.1 1.6 5.2 //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25825 SUBJECT: LIGO/Virgo S190923y: INTEGRAL IBIS coded-masked imaging observations of part of the localization area and further all-sky upper limits DATE: 19/09/23 21:44:09 GMT FROM: Antonio Martin-Carrillo at UCD,Space Science Group Antonio Martin-Carrillo (UCD), Francesca Onori, 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 At the time of the event S190923y (2019-09-23 12:55:59 UTC, GCN 25814) and based on the initial localization map, 8% of the LIGO/Virgo GW localization was within the field of view of IBIS. The background within +/-300 seconds around the event was very stable (excess variance 1.1). Initial analysis of the pointed observations of IBIS do not reveal any relevant counterparts at this point. 3-sigma upper limits of about 5e-10erg/cm2/s (28-40 keV energy range) in single pointings of about 30 min at ~T0+5.5h have been found in areas at the edge of the 90% LIGO/Virgo contour. INTEGRAL will continue to serendipitously observe the localization area of S190923y over the nex few hours. Any relevant candidates will be reported separately. We have included this new data to the initial results presented in Onori et al (GCN 25815) to search for any impulsive events in INTEGRAL SPI- ACS (as described in [1]), IBIS, and IBIS/Veto data. We do not detect any significant counterparts and estimate a 3-sigma upper limit on the 75-2000 keV fluence of 3.4e-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 ~3.4e-07 (3.7e-08) erg/cm^2/s at 1 s (8 s) time scale in 75-2000 keV energy range. For the mean reported distance 438.0 Mpc this corresponds to the limit on the total isotropic equivalent energy in 1 s of 7.8e+48 erg for the short GRB spectrum and for a long GRB spectrum isotropic equivalent luminosity in 1 s (8 s) of 2.6e+48 erg/s (8.6e+47 erg/s) These upper limits take into account that the peak of the event localization probability was at an angle of 158 deg with respect to the spacecraft pointing axis at the time of the trigger. This orientation implies strongly suppressed (3.2% of optimal) response of ISGRI, somewhat suppressed (62% of optimal) response of IBIS/Veto, and somewhat suppressed (43% of optimal) response of SPI-ACS. All results quoted are preliminary. This circular is an official product of the INTEGRAL Multi-Messenger team. [1] Savchenko et al. 2012, A&A 541A, 122S //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25830 SUBJECT: LIGO/Virgo S190923y: Upper limits from CALET observations. DATE: 19/09/24 03:19:03 GMT FROM: Yuta Kawakubo at Louisiana State U./CALET A. Yoshida, T. Sakamoto, V. Pal'shin, S. Sugita (AGU), Y. Kawakubo (LSU), K. Yamaoka (Nagoya U), S. Nakahira (RIKEN), Y. Asaoka, 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 S190923y T0 = 2019-09-23 12:55:59.646 UT (The LIGO Scientific Collaboration and Virgo Collaboration, GCN Circ. 25814). 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 40 % and 55 %, respectively (and 68 % credible region of the initial sky map was above the horizon). The HXM and SGM fields of view were centered at RA = 62.7 deg, Dec = 4.2 deg and RA = 55.3 deg, Dec = -2.5 deg at T0, respectively. Based on the analysis of the light curve data with 0.125 sec time resolution from T0-60 sec to T0+60 sec, we found no significant excess around the trigger time in either the HXM or the SGM data. The CALET Calorimeter (CAL) was operating in the high energy trigger mode at the trigger time of S190923y. Using the CAL data, we have searched for gamma-ray events in the 10-100 GeV band from -60 sec to +60 sec from the GW trigger time and found no candidates in the overwrap region with the LIGO-Virgo high probability localization region. The 90% upper limit of CAL is 1.2x10^-5 erg/cm^2/s (10-100 GeV) when the summed LIGO-Virgo probability reaches 10%. The CAL FOV was centered at RA= 55.3 deg, DEC= -2.5 deg at T0. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25834 SUBJECT: LIGO/Virgo S190923y: No counterpart candidates in Fermi-LAT observations DATE: 19/09/24 04:36:16 GMT FROM: Magnus Axelsson at Stockholm U. F. Longo (Univ. and INFN Trieste), E. Bissaldi (Politecnico and INFN Bari), E. Moretti (IFAE, Barcelona), M. Moss (George Washington Univ.), N. Omodei (Stanford Univ.), D. Kocevski (NASA/MSFC) and M. Axelsson (KTH and Stockholm Univ.) report on behalf of the Fermi-LAT Collaboration: We have searched data collected by the Fermi Large Area Telescope (LAT) on Sep 23, 2019, for possible high-energy (E > 100 MeV) gamma-ray emission in spatial/temporal coincidence with the LIGO/Virgo trigger S190923y (GCN 25814). 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 an instantaneous coverage of ~40% of the LIGO probability region at the time of the trigger (T0 = 2019-09-23 12:55:59.646 UTC) and reached 100% cumulative coverage at approximately T0 + 8.8 ks. 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 1.3e-10 and 1.4e-9 [erg/cm^2/s]. The Fermi-LAT point of contact for this event is Elena Moretti (emoretti@ifae.es). 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: 25842 SUBJECT: LIGO/Virgo S190923y: No neutrino candidates at Pierre Auger Observatory DATE: 19/09/24 20:29:37 GMT FROM: Jaime Alvarez-Muniz at Pierre Auger Observatory J. Alvarez-Muniz, F. Pedreira, E. Zas (IGFAE & University of Santiago de Compostela, Spain), K. H. Kampert & M. Schimp (University of Wuppertal, Germany) on behalf of the Pierre Auger Collaboration. In response to: LIGO/Virgo GW trigger S190923y T0=2019-09-23 12:55:59 UTC We searched for Ultra-High-Energy (UHE) neutrinos with energies above ~ 1e17 eV in data collected with the Surface Detector (SD) of the Pierre Auger Observatory in a [-500,500] second interval about the LIGO-Virgo trigger S190923y as well as in a 24 hr time interval following the event. NO events survived the cuts applied to reject the background due to UHE Cosmic Rays i.e. NO neutrino candidates were detected. The field of view (fov) where the SD of Auger is sensitive to UHE neutrinos (corresponding to inclined directions with respect to the vertical relative to the ground) was PARTIALLY COINCIDENT (68.2%) with the LIGO/Virgo 90% localization region (bayestar.fits.gz,0) at the time T0 of the merger alert, achieving TOTAL OVERLAP at approximately T0+1.36 hours. ------- The Pierre Auger Observatory is an UHE Cosmic Ray detector located in the Mendoza Province in Argentina. It consists of an array of Water Cherenkov detectors spread over a total surface of 3000 km^2 arranged in a triangular grid of 1.5 km side as well as Fluorescence telescopes and other systems (see 10.1016/j.nima.2015.06.058 for more information). For neutrino searches from GW events with Auger, please refer to: https://journals.aps.org/prd/pdf/10.1103/PhysRevD.94.122007 https://arxiv.org/abs/1906.07422 //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25846 SUBJECT: LIGO/Virgo S190923y: no counterpart candidates in the Swift/BAT observations DATE: 19/09/26 01:33:47 GMT FROM: Amy Lien at GSFC T. Sakamoto (AGU), S. D. Barthelmy (NASA/GSFC), A. Y. Lien (GSFC/UMBC), D. M. Palmer (LANL), 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), N. Klingler (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 (Toronto), 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 S190923y (LIGO/VIRGO Collaboration GCN Circ. 25814), where T0 is the LVC trigger time (2019-09-23T12:55:59.645 UTC). The center of the BAT field of view (FOV) at T0 is RA = 5.951 deg, DEC = -1.780 deg, and the roll angle is 107.879 deg. The BAT FOV (>10% partial coding) covers 0.00% of the integrated LVC localization probability, and 0.00% of the galaxy convolved probability (Evans et al. 2016). Note that the sensitivity in the BAT FOV changes with the partial coding fraction. Please see the BAT FOV figure in the summary page (link below) for the specific location of the LVC region relative to the BAT FOV. 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 ~ 7.56 x 10^-8 erg/s/cm^2. Assuming a luminosity of ~ 2 x 10^47 erg/s (similar to GW170817) and an average Epeak of ~ 400 keV for short GRBs (Bhat et al. 2016), this flux upper limit corresponds to a distance of ~ 82.64 Mpc. Event data are available from T0-101.32 to T+98.757. No significant detections are found in the 15-350 keV images created using intervals of T0 to T0+0.1 s, T0-2 s to T0+8 s, and the whole event data range. BAT retains decreased, but significant, sensitivity to rate increases for gamma-ray events outside of its FOV. About 99.92% 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/S190923y/web/source_public.html //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25847 SUBJECT: LIGO/Virgo S190923y: No significant candidates in TAROT-GRANDMA observations DATE: 19/09/26 01:48:57 GMT FROM: Damien Turpin at NAOC (CAS) D. Turpin (NAOC), P. Hello (LAL), K. Noysena (Artemis, IRAP), C. Thoene (HETH/IAA-CSIC), M. Boer (Artemis), N. Christensen (Artemis), L. Eymar (Artemis), A. Klotz (IRAP), S. Antier (APC), S. Basa (LAM), D. Corre (LAL), M. Coughlin (Caltech), D. Coward (OzGrav-UWA), J.G. Ducoin (LAL), B. Gendre (OzGrav-UWA), D. A. Kann (HETH/IAA-CSIC), C. Lachaud (APC), N. Leroy (LAL) report on behalf of the TAROT network and GRANDMA collaborations: We performed tiled observations of the LIGO/Virgo S190923y event with the TAROT-Reunion (TRE), TAROT-Calern (TCA) and TAROT-Chili (TCH) telescopes operating in the visible located respectively at Les Makes astronomical observatory, the Cote d'Azur observatory and La Silla ESO observatory (LaS/ESO). The observation started on 09/23/19 16:30:12 UTC for TRE which corresponds approximately to 215 minutes after the GW trigger time. For TCA it started on 09/23/19 18:22:31 UTC which corresponds approximately to 327 minutes after the GW trigger time. For TCH it started on 09/23/19 23:42:17 UTC which corresponds approximately to 647 minutes after the GW trigger time. We performed the following tiled observations : +-------+------------+------------+---------+---------+---------+ | Tele  | TStart     | TEnd       | RA      | DEC     |   Proba | | scope | [UTC]      | [UTC]      | [deg]   | [deg]   |     [%] | |-------|------------+------------+---------+---------+---------| |  TRE  | 2019-09-23 | 2019-09-25 | 250.909 | -40.909 |     1.2 | |       | 16:30:12   | 18:18:14   |         |         |         | |  TRE  | 2019-09-23 | 2019-09-25 | 243.243 | -32.727 |     1.1 | |       | 16:43:24   | 16:01:15   |         |         |         | |  TRE  | 2019-09-23 | 2019-09-25 | 243.117 | -28.636 |     1.1 | |       | 16:55:50   | 16:13:27   |         |         |         | |  TRE  | 2019-09-23 | 2019-09-25 | 245.455 | -40.909 |     1   | |       | 17:08:55   | 16:26:45   |         |         |         | |  TRE  | 2019-09-23 | 2019-09-25 | 285     | -73.636 |     0.8 | |       | 17:21:15   | 19:09:01   |         |         |         | |  TRE  | 2019-09-23 | 2019-09-25 | 243     | -24.545 |     0.8 | |       | 17:40:29   | 16:58:26   |         |         |         | |  TRE  | 2019-09-23 | 2019-09-25 | 256.154 | -53.182 |     1.6 | |       | 17:56:56   | 17:33:16   |         |         |         | |  TRE  | 2019-09-23 | 2019-09-25 | 249.677 | -45     |     1.5 | |       | 18:16:07   | 17:52:26   |         |         |         | |  TRE  | 2019-09-23 | 2019-09-25 | 246.857 | -36.818 |     1.4 | |       | 18:29:19   | 18:05:44   |         |         |         | |  TRE  | 2019-09-23 | 2019-09-25 | 276     | -69.545 |     1   | |       | 19:13:36   | 21:19:48   |         |         |         | |  TRE  | 2019-09-23 | 2019-09-25 | 265.714 | -61.364 |     1.2 | |       | 21:05:15   | 20:41:36   |         |         |         | |  TRE  | 2019-09-23 | 2019-09-25 | 270     | -65.455 |     1.2 | |       | 21:17:59   | 20:54:39   |         |         |         | |  TRE  | 2019-09-23 | 2019-09-25 | 90      | 4.091   |     1.1 | |       | 21:35:17   | 23:37:06   |         |         |         | |  TRE  | 2019-09-23 | 2019-09-26 | 85.909  | 0       |     1   | |       | 21:56:18   | 00:02:43   |         |         |         | |  TRE  | 2019-09-23 | 2019-09-25 | 85.909  | 4.091   |     0.8 | |       | 22:15:29   | 21:51:45   |         |         |         | |  TRE  | 2019-09-23 | 2019-09-25 | 91.034  | 8.182   |     1.5 | |       | 23:09:44   | 22:46:17   |         |         |         | |  TRE  | 2019-09-24 | 2019-09-24 | 248.108 | -32.727 |     0.7 | |       | 18:28:15   | 18:34:32   |         |         |         | |  TRE  | 2019-09-24 | 2019-09-25 | 260.425 | -57.273 |     1.4 | |       | 19:22:29   | 20:24:29   |         |         |         | |-------|------------+------------+---------+---------+---------| |  TCA  | 2019-09-23 | 2019-09-25 | 150.95  | 48.27   |     0.1 | |       | 18:22:31   | 02:58:48   |         |         |         | |  TCA  | 2019-09-23 | 2019-09-25 | 89.075  | 11.156  |     0.1 | |       | 23:41:57   | 03:19:06   |         |         |         | |  TCA  | 2019-09-24 | 2019-09-24 | 81.575  | -9.256  |     0.1 | |       | 00:27:20   | 03:03:58   |         |         |         | |  TCA  | 2019-09-24 | 2019-09-24 | 80.112  | -11.112 |     0.1 | |       | 00:40:21   | 00:46:41   |         |         |         | |  TCA  | 2019-09-24 | 2019-09-26 | 79.7    | -9.256  |     0.1 | |       | 00:47:07   | 00:23:08   |         |         |         | |  TCA  | 2019-09-24 | 2019-09-26 | 92.783  | 3.733   |     0.1 | |       | 00:53:52   | 00:29:56   |         |         |         | |  TCA  | 2019-09-24 | 2019-09-25 | 146.538 | 46.414  |     0.2 | |       | 01:26:35   | 02:32:55   |         |         |         | |  TCA  | 2019-09-24 | 2019-09-25 | 149.185 | 46.414  |     0.2 | |       | 01:33:22   | 02:35:21   |         |         |         | |  TCA  | 2019-09-24 | 2019-09-25 | 151.832 | 46.414  |     0.2 | |       | 01:40:06   | 02:46:24   |         |         |         | |  TCA  | 2019-09-24 | 2019-09-25 | 148.223 | 48.27   |     0.1 | |       | 01:59:17   | 03:05:36   |         |         |         | |  TCA  | 2019-09-24 | 2019-09-25 | 145.495 | 48.27   |     0.1 | |       | 02:06:01   | 03:12:21   |         |         |         | |  TCA  | 2019-09-24 | 2019-09-24 | 142.768 | 48.27   |     0.1 | |       | 02:18:25   | 02:24:45   |         |         |         | |  TCA  | 2019-09-24 | 2019-09-25 | 153.677 | 48.27   |     0.1 | |       | 02:25:12   | 18:31:12   |         |         |         | |  TCA  | 2019-09-24 | 2019-09-25 | 156.405 | 48.27   |     0.1 | |       | 02:31:57   | 18:38:00   |         |         |         | |  TCA  | 2019-09-24 | 2019-09-25 | 83.022  | -7.401  |     0.1 | |       | 02:38:42   | 01:14:45   |         |         |         | |  TCA  | 2019-09-24 | 2019-09-25 | 159.132 | 48.27   |     0.1 | |       | 02:50:52   | 18:57:10   |         |         |         | |  TCA  | 2019-09-24 | 2019-09-25 | 147.433 | 42.703  |     0.1 | |       | 03:04:26   | 04:08:35   |         |         |         | |  TCA  | 2019-09-24 | 2019-09-25 | 161.859 | 48.27   |     0.1 | |       | 03:30:18   | 02:06:41   |         |         |         | |-------+------------+------------+---------+---------+---------+ |  TCH  | 2019-09-23 | 2019-09-25 | 261.239 | -54.505 |     0.2 | |       | 23:42:17   | 03:18:23   |         |         |         | |  TCH  | 2019-09-24 | 2019-09-25 | 251.119 | -52.686 |     0.2 | |       | 00:03:52   | 23:38:03   |         |         |         | |  TCH  | 2019-09-24 | 2019-09-25 | 243.214 | -36.323 |     0.2 | |       | 00:08:26   | 23:44:47   |         |         |         | |  TCH  | 2019-09-24 | 2019-09-26 | 265.656 | -69.05  |     0.1 | |       | 00:34:28   | 00:10:43   |         |         |         | |  TCH  | 2019-09-24 | 2019-09-25 | 239.646 | -21.777 |     0.2 | |       | 02:05:45   | 00:41:50   |         |         |         | |  TCH  | 2019-09-24 | 2019-09-25 | 239.014 | -19.959 |     0.2 | |       | 02:24:51   | 01:01:21   |         |         |         | |  TCH  | 2019-09-24 | 2019-09-25 | 285.466 | -70.868 |     0.2 | |       | 02:50:54   | 23:57:11   |         |         |         | |  TCH  | 2019-09-24 | 2019-09-26 | 296.15  | -74.505 |     0.1 | |       | 03:29:45   | 00:36:07   |         |         |         | |  TCH  | 2019-09-24 | 2019-09-25 | 265.656 | -58.141 |     0.2 | |       | 05:14:24   | 06:20:43   |         |         |         | |  TCH  | 2019-09-24 | 2019-09-25 | 93.211  | 5.495   |     0.2 | |       | 05:53:19   | 06:59:50   |         |         |         | |  TCH  | 2019-09-24 | 2019-09-25 | 92.787  | 10.95   |     0.4 | |       | 06:26:33   | 07:32:51   |         |         |         | |  TCH  | 2019-09-24 | 2019-09-25 | 94.624  | 10.95   |     0.4 | |       | 06:33:19   | 07:39:36   |         |         |         | |  TCH  | 2019-09-24 | 2019-09-25 | 90.95   | 10.95   |     0.3 | |       | 06:40:04   | 07:46:20   |         |         |         | |  TCH  | 2019-09-24 | 2019-09-25 | 94.148  | 9.132   |     0.3 | |       | 06:46:48   | 07:53:05   |         |         |         | |  TCH  | 2019-09-24 | 2019-09-25 | 96.46   | 10.95   |     0.2 | |       | 07:01:09   | 08:05:28   |         |         |         | |  TCH  | 2019-09-24 | 2019-09-25 | 94.07   | 7.314   |     0.2 | |       | 07:18:38   | 08:24:58   |         |         |         | |  TCH  | 2019-09-25 | 2019-09-26 | 239.793 | -27.707 |     0.2 | |       | 01:27:40   | 00:03:57   |         |         |         | |  TCH  | 2019-09-25 | 2019-09-25 | 242.134 | -21.777 |     0.1 | |       | 01:46:49   | 01:53:08   |         |         |         | |-------+------------+------------+---------+---------+---------+ TStart and TEnd refers respectively to the time of the first and last exposure for a given tile. Observations are not necessarily continuous in this interval. The Probability refers to the 2D spatial probability of the GW skymap enclosed in a given tile. Each TRE tile is 4.2x4.2 degrees and 1.9x1.9 degrees for TCA and TCH. These observations cover about 25.5% the cumulative probability of the Bayestar skymap available on Sep 23, 2019 13:01:56 UTC. The typical limiting magnitude is 17.0 and 18.0 for a 60.0 s exposure for TRE and TCA/TCH, respectively. The coverage map is available at: https://grandma-owncloud.lal.in2p3.fr/index.php/s/Y2sXYjRmkubuRrw No significant transient candidates were found during our low latency analysis. GRANDMA (Global Rapid Advanced Network Devoted to the Multi-messenger Addicts) is a network of robotic telescopes connected all over the world with both photometry and spectroscopy capabilities for Time- domain Astronomy (https://grandma.lal.in2p3.fr/). Details on the TRE, TCA and TCH telescopes are available on the GRANDMA web pages or on  http://tarot.obs-hp.fr/. This circular is citable. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25855 SUBJECT: LIGO/Virgo S190923y: MASTER OT outburst detection inside NSBH merger error-box DATE: 19/09/27 15:44:16 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs V. Lipunov, E. Gorbovskoy, V.Kornilov, N.Tiurina, P.Balanutsa,A.Kuznetsov, V.Vladimirov, D. Vlasenko, I.Gorbunov,D.Zimnukhov, V.Senik, T.Pogrosheva, K.Pozdnyakov, A.Chasovnikov, V.Topolev, F.Balakin, 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 started LIGO/Virgo S190923y (Minazzoli et al. LVC GCN 25814, Ttrig = 2019-09-23 12:55:59.646 UT) inspection 374 sec after notice time (798 sec after trigger time) at 2019-09-23 13:09:17 UT (Lipunov et al. GCN 25812) https://master.sai.msu.ru/site/master2/ligo_1.php?id=10825 . MASTER OT J162250.41-482250.3 discovery MASTER-SAAO auto-detection system ( Lipunov et al., "MASTER Global Robotic Net", Advances in Astronomy, 2010, 30L ) discovered OT source at (RA, Dec) = 16h 22m 50.41s -48d 22m 50.3s on 2019-09-26.80632 UT (AT 2019rfj). The OT unfiltered magnitude is 17.0m (mlim=18.6). The OT is seen on 2 images on 2019-09-26 19:33:10, 19:21:06UT in MASTER-SAAO and on 4 images on 2019-09-27 00:12:12-00:30:55 in MASTER-OAFA. There is no minor planet at this place. We have reference images on 2019-09-23.89472 UT (nearest in time) with unfiltered mlim=18.2m. Spectral observations are required. The discovery and reference images are available at: http://master.sai.msu.ru/static/OT/162250.41-482250.3.png The observation and reduction will be continued. The message may be cited. //////////////////////////////////////////////////////////////////////// TITLE: GCN CIRCULAR NUMBER: 25903 SUBJECT: LIGO/Virgo S190923y: optical spectrum of MASTER detected transient DATE: 19/10/01 17:48:12 GMT FROM: Marina Orio at INAF-Padova and U of Wisconsin David Buckley (South African Astronomical Observatory), Stefano Ciroi (Padova University), Marina Orio (Istituto Nazionale di Astrofisica-Padova, and University of Wisconsin), Saurabh Jah (Rutgers University) and Joanna Mikolajewska (Nicolaus Copernicus Center of the PAS) report: On 2019/9/27 at UT 17:48:22 we obtained an optical spectrum of the transient source MASTER OT J162250.41-482250.3 discovered by the MASTER Global Robotic Net in the field of the gravitational wave event S190923y (see GCN 25855) , with the Robert Stobie spectrograph on the SALT telescope and the PG 300 grating, in the 3300-9800 Angstrom range and with a 22 Angstrom spectral resolution. The spectrum has a blue continuum and various emission lines, of which the most prominent is H-alpha. Several other emission lines of He I and He at 4686 Angstrom are also detected, and all spectral lines do not show significant red shift. We measured the following equivalent widths: He II 4686 Angstrom: 0.71 Angstrom Hbeta 0.79 Angstrom He I 5876 Angstrom 1.02 Angstrom Halpha 10.12 Angstrom He I 6678 Angstrom 1.93 Angstrom He I 7065 Angstrom 1.73 Angstrom The spectrum is consistent with a Galactic source, likely to be a cataclysmic variable or another low mass binary in outburst. This result rules out that this transient as the optical counterpart of the gravitational wave event.