TITLE: GCN CIRCULAR NUMBER: 21063 SUBJECT: LIGO/Virgo G284239: INTEGRAL search for a prompt gamma-ray counterpart DATE: 17/05/03 21:00:24 GMT FROM: Volodymyr Savchenko at APC,Paris V. Savchenko (ISDC, University of Geneva, CH) on behalf of the INTEGRAL group: S. Mereghetti (IASF-Milano, Italy), C. Ferrigno ((ISDC, University of Geneva, CH), E. Kuulkers (ESTEC/ESA, The Netherlands), A. Bazzano (IAPS-Roma, Italy), E. Bozzo, T. J.-L. Courvoisier (ISDC, University of Geneva, CH) S. Brandt (DTU - Denmark) R. Diehl (MPE-Garching, Germany) L. Hanlon (UCD, Ireland) P. Laurent (APC, Saclay/CEA, France) A. Lutovinov (IKI, Russia) J.P. Roques (CESR, France) R. Sunyaev (IKI, Russia) P. Ubertini (IAPS-Roma, Italy) We investigated serendipitous INTEGRAL observations carried out at the time of the LIGO/Virgo burst candidate G284239. The satellite was pointing at RA=294.829 Dec=17.726, far from the high-probability area of LIGO localization. For the full LIGO 90% confidence region the best upper limit is set by the anti-coincidence shield of the spectrometer on board of INTEGRAL (SPI/ACS). The INTEGRAL Burst Alert System (IBAS) did not identify any unusual transients in coincidence with the LIGO/Virgo trigger. The IBAS inspects both ISGRI Field of View and all-sky SPI-ACS light curve. We investigated the SPI-ACS, IBIS/Veto, and IBIS/ISGRI light curves between -500 and +500 s from the trigger time (2017-05-02 22:26:07 UTC) on temporal scales from 0.1 to 100 s, and found no evidence for any deviation from the background. We estimate combined typical 3-sigma upper limits of 3.7e-7 erg/cm2 (75-2000 keV) for 8s duration assuming Band model parameters alpha=-1, beta=-2.5, and E_ peak = 300 keV. To derive a limit for a typical short burst with 1 s duration, we use a harder cutoff power law spectrum with a photon index of -0.5 and an Epeak = 500 keV. We find a limiting fluence of 1.5e-7 erg/cm2 (75-2000 keV) at 3 sigma c.l. These limits assume a perpendicular direction of the burst to the INTEGRAL pointing direction, optimal for SPI-ACS sensitivity. However the extent of the region with optimal response depends on the possible source spectrum: we perform a detailed calculation only for a cutoff powerlaw spectrum with a photon index of -0.5 and an Epeak = 500 keV. We estimate that 60% of the LIGO localization probability is covered with a range of sensitivity from optimal for SPI-ACS (mentioned above) to 50% worse than optimal. The 90% LIGO confidence region includes a small area for which the SPI-ACS sensitivity is unusually strongly suppressed. The region in which SPI-ACS sensitivity is reduced more than by factor 3 contains about 10% of LIGO localization probability.