{
  "bibcode": "2017GCN.20694....1S",
  "body": "V. Savchenko (ISDC, University of Geneva, CH)\non behalf of the INTEGRAL group: S. Mereghetti (IASF-Milano, Italy),\nC. Ferrigno ((ISDC, University of Geneva, CH), E. Kuulkers (ESTEC/ESA, \nThe Netherlands),\nA. Bazzano (IAPS-Roma, Italy), E. Bozzo, T. J.-L. Courvoisier (ISDC, \nUniversity of Geneva, CH)\nS. Brandt (DTU - Denmark) R. Diehl (MPE-Garching, Germany) L. Hanlon \n(UCD, Ireland)\nP. Laurent (APC, Saclay/CEA, France) A. Lutovinov (IKI, Russia) J.P. \nRoques (CESR, France)\nR. Sunyaev (IKI, Russia) P. Ubertini (IAPS-Roma, Italy)\n\nWe investigated serendipitous INTEGRAL observations carried out at the time\nof the LIGO/Virgo burst candidate G274296. The satellite was pointing at\nRA=17:30:10.94 Dec=-25:04:47.6, close to the low-probability area of \nLIGO localization.\nAbout 2% of the probability was contained in the field of view of \nINTEGRAL IBIS and SPI.\nDepending on the location within the LIGO 90% localization region, as \nwell as the assumed\ncounterpart spectrum and duration, the best upper limit is set by the \nanti-coincidence shield\nof the spectrometer on board of INTEGRAL (SPI/ACS), the anti-coincidence \nshield of\nthe IBIS instrument (IBIS/Veto), or by the imaging coded mask \ninstruments (IBIS and SPI).\nThe combination of these instruments covered the full LIGO 90% \nconfidence region and\nprovided stringent constraints on the flux of a possible electromagnetic \ncounterpart\nin the energy range covered by the INTEGRAL instruments.\n\nWe investigated the SPI-ACS, IBIS/Veto, and IBIS/ISGRI light curves between\n-500 and +500 s from the trigger time (2017-02-17 06:05:53 UTC) on \ntemporal scales\nfrom 0.1 to 100 s, and found no evidence for any deviation from the \nbackground.\nWe estimate combined typical 3-sigma upper limits of  3.8e-7 erg/cm2 \n(75-2000 keV)\nfor 8s duration assuming Band model parameters alpha=���1, beta=���2.5, and \nE_ peak = 300 keV.\nTo derive a limit for a typical short burst with 1 s duration, we use a \nharder cutoff\npower law spectrum with a slope of ���0.5 and an Epeak = 500 keV: we find \na limiting fluence\nof 1.4e-7 erg/cm2 (75-2000 keV) at 3 sigma c.l.. These limits assume a \nperpendicular\ndirection of the burst to the INTEGRAL pointing direction, optimal for \nSPI-ACS sensitivity.\nHowever the extent of the region with optimal response depends on the \npossible source spectrum:\nwe perform a detailed calculation only for a cutoff powerlaw spectrum \nwith a slope of ���0.5 and\nan Epeak = 500 keV: we estimate that 35% of the LIGO localization \nprobability region is covered\nwith a range of sensitivity from optimal for SPI-ACS (mentioned above) \nto 50% worse. About 2%\nof the LIGO localization in the field of view of IBIS and SPI is covered \nwith at least\nfactor 2 better sensitivity.\n\nThe SPI/ACS light curves, binned at 50 ms, are derived from 91 \nindependent detectors with different\nlower energy thresholds (mainly between 50 keV and 150 keV) and an upper \nthreshold at about 100 MeV.\nThe ACS response varies substantially as a function of the source \nincident angle with an optimal\neffective area of about 6000 cm2 at 1 MeV.",
  "circularId": 20694,
  "createdOn": 1487452095000,
  "email": "savchenk@apc.in2p3.fr",
  "subject": "LIGO/Virgo G274296: INTEGRAL search for a prompt gamma-ray counterpart",
  "submitter": "Volodymyr Savchenko at APC,Paris  <savchenk@apc.in2p3.fr>",
  "eventId": "LIGO/Virgo G274296"
}