{
  "bibcode": "2017GCN.21063....1S",
  "body": "V. Savchenko (ISDC, University of Geneva, CH)\non behalf of the INTEGRAL group:\nS. Mereghetti (IASF-Milano, Italy),\nC. Ferrigno ((ISDC, University of Geneva, CH),\nE. Kuulkers (ESTEC/ESA, The Netherlands),\nA. Bazzano (IAPS-Roma, Italy), E. Bozzo,\nT. J.-L. Courvoisier (ISDC, University of Geneva, CH)\nS. Brandt (DTU - Denmark) R. Diehl (MPE-Garching, Germany)\nL. Hanlon (UCD, Ireland) P. Laurent (APC, Saclay/CEA, France)\nA. Lutovinov (IKI, Russia) J.P. Roques (CESR, France)\nR. Sunyaev (IKI, Russia) P. Ubertini (IAPS-Roma, Italy)\n\nWe investigated serendipitous INTEGRAL observations carried out at the\ntime of the LIGO/Virgo burst candidate G284239.  The satellite was\npointing at RA=294.829 Dec=17.726, far from the high-probability area of \nLIGO\nlocalization. For the full LIGO 90% confidence region the best upper\nlimit is set by the anti-coincidence shield of the spectrometer on board\nof INTEGRAL (SPI/ACS).\n\nThe INTEGRAL Burst Alert System (IBAS) did not identify any unusual\ntransients in coincidence with the LIGO/Virgo trigger. The IBAS\ninspects both ISGRI Field of View and all-sky SPI-ACS light curve.\n\nWe investigated the SPI-ACS, IBIS/Veto, and IBIS/ISGRI light curves\nbetween -500 and +500 s from the trigger time (2017-05-02 22:26:07\nUTC) on temporal scales from 0.1 to 100 s, and found no evidence for\nany deviation from the background.  We estimate combined typical\n3-sigma upper limits of 3.7e-7 erg/cm2 (75-2000 keV) for 8s duration\nassuming Band model parameters alpha=-1, beta=-2.5, and E_ peak = 300\nkeV.  To derive a limit for a typical short burst with 1 s duration,\nwe use a harder cutoff power law spectrum with a photon index of -0.5\nand an Epeak = 500 keV. We find a limiting fluence of 1.5e-7 erg/cm2\n(75-2000 keV) at 3 sigma c.l. These limits assume a perpendicular\ndirection of the burst to the INTEGRAL pointing direction, optimal for\nSPI-ACS sensitivity. However the extent of the region with optimal\nresponse depends on the possible source spectrum: we perform a\ndetailed calculation only for a cutoff powerlaw spectrum with a photon\nindex of -0.5 and an Epeak = 500 keV. We estimate that 60% of the LIGO\nlocalization probability is covered with a range of sensitivity from\noptimal for SPI-ACS (mentioned above) to 50% worse than optimal. The\n90% LIGO confidence region includes a small area for which the SPI-ACS\nsensitivity is unusually strongly suppressed. The region in which\nSPI-ACS sensitivity is reduced more than by factor 3 contains about\n10% of LIGO localization probability.",
  "circularId": 21063,
  "createdOn": 1493845224000,
  "email": "savchenk@apc.in2p3.fr",
  "subject": "LIGO/Virgo G284239: INTEGRAL search for a prompt gamma-ray counterpart",
  "submitter": "Volodymyr Savchenko at APC,Paris  <savchenk@apc.in2p3.fr>",
  "eventId": "LIGO/Virgo G284239"
}