TITLE: GCN CIRCULAR NUMBER: 21231 SUBJECT: LIGO/Virgo G288732: INTEGRAL search for a prompt gamma-ray counterpart DATE: 17/06/09 08:35:07 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 G288732. The satellite was pointing at RA=180.649, Dec=-60.391, far from the high-probability area of LIGO localization. Depending on the location within the LIGO localization region, as well as the assumed counterpart spectrum and duration, the best upper limit is set by the anti-coincidence shield of the spectrometer on board of INTEGRAL (SPI/ACS) or by the anti-coincidence shield of the IBIS instrument (IBIS/Veto). The combination of these instruments covered the full LIGO localization region and provided constraints on the flux of a possible electromagnetic counterpart in the energy range covered by the INTEGRAL instruments, although the localization was somewhat unfavorable for the INTEGRAL observation. 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 and IBIS/Veto light curves between -500 and +500 s from the trigger time (2017-06-08 02:01:16.5 UTC) on temporal scales from 0.1 to 100 s, and found no evidence for any deviation from the background. We estimate a 3-sigma fluence upper limit enclosing 90% of LIGO probability of 1.65e-6 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 and we find a limiting fluence of 4.3e-7 erg/cm2 (75-2000 keV) at 3 sigma c.l. This limit applies to 90% of LIGO localization probability.