{
  "bibcode": "2017GCN.21672....1S",
  "body": "V. Savchenko (ISDC, University of Geneva, CH)\nC. Ferrigno, E. Bozzo ((ISDC, University of Geneva, CH),\nE. Kuulkers (ESTEC/ESA, The Netherlands),\nS. Mereghetti (IASF-Milano, Italy),\nT. J.-L. Courvoisier (ISDC, University of Geneva, CH)\nJ. Chenevez, S. Brandt (DTU, Denmark)\nR. Diehl (MPE-Garching, Germany)\nL. Hanlon (UCD, Ireland)\nP. Laurent, D. Gotz (APC, Saclay/CEA, France)\nJ.P. Roques, E. Jourdain (IRAP, France)\nP. Ubertini, A. Bazzano, J. Rodi (IAPS-Roma, Italy)\nA. Lutovinov, R. Sunyaev (IKI, Russia)\n\nINTEGRAL is an observatory with multiple instruments: a gamma-ray\nspectrometer (20 keV - 8 MeV, SPI), an imager (15 keV - 2 MeV, IBIS),\nan X-ray monitor (3 - 25 keV, JEM-X), and an optical monitor (V band,\nOMC). Our group requested and obtained follow-up observations of the\nLIGO/Virgo candidate NS merger G298048 (GCN 21505, 21506).\n\nThe initial observation was centered on the best Fermi/GBM\nlocalization, RA=176.8, Dec=-39.8 (GCN 21509), and was carried out\nfrom 2017-08-18 08:17:51 to 2017-08-18 12:36:11 for a total observing\ntime of 14.8 ks. It covered 72% of the Fermi/GBM localization\nprobability but only a negligible fraction of the current LIGO/Virgo\nlocalization. We do not detect any new sources in the complete\nIBIS/ISGRI (20-80 keV and 80 - 300 keV) and JEM-X (3-10 keV, 10 - 25\nkeV) mosaicked images, with a best sensitivity of 7.9 mCrab (1.2e-7\nerg/cm2/s) in the 20 - 80 keV energy range.\n\nThe main part of the INTEGRAL follow-up observation was centered on\nthe candidate optical counterpart SSS17a (RA=13:09:48.089\nDec=-23:22:53.35; GCN 21529).  This observation spanned from\n2017-08-18 12:45:10 to 2017-08-23 04:07:47 (starting about 24 hours\nafter the LIGO/Virgo event), with a maximum on-source time of about\n330 ks (depending on the instrument).\n\nSSS17a was in IBIS and SPI FoV in each of the dithered single pointing\nthat make up an INTEGRAL observations; whilst it was in the JEM-X FoV\nonly a fraction of the time.\n\nWe investigated the complete observation mosaics of ISGRI, SPI, and\nJEM-X data. INTEGRAL provides the most stringent constraint on any\npossible emission associated with SSS17a above 80 keV. We do not\ndetect the source in any energy ranges of any of the INTEGRAL\ninstruments, and set the following 3-sigma upper bounds for an average\nflux of a source at the position of SSS17a:\n\nJEM-X:\n\n3-10 keV:       1.2 mCrab (1.9e-11 erg/cm2/s )\n10-25 keV:      0.64 mCrab (7e-12 erg/cm2/s )\n\nISGRI:\n\n20-80 keV:      2.6 mCrab (3.8e-11 erg/cm2/s)\n80-300 keV:     6.2 mCrab (7.1e-11 erg/cm2/s)\n300-500 keV:    291.6 mCrab (1e-9 erg/cm2/s)\n\nSPI:\n\n20 - 80 keV:    7.2 mCrab (1.1e-10 erg/cm2/s)\n80 - 300 keV:   24 mCrab (2.8e-10 erg/cm2/s)\n300 - 500 keV:  175 mCrab (6.1e-10 erg/cm2/s)\n500 - 1000 keV: 770 mCrab (3.1e-9 erg/cm2/s)\n1 MeV - 2 MeV:  1.0 Crab (3.3e-9 erg/cm2/s)\n\nWe have also searched for isolated line-like features in ISGRI and SPI\ndata, and preliminary analysis did not identify any such\nfeatures. Further analysis is ongoing.\n\nIBIS, SPI, and JEM-X observed more than 97% of the of LIGO\nlocalization in the combined observation mosaic.  We searched\nIBIS/ISGRI and JEM-X data for any new point source in the whole 90%\nLIGO/Virgo localization region, and did not find any. The sensitivity\ndepends on the location, with the best value close to that computed\nfor SSS17a.\n\nContinuous observation provided by INTEGRAL allows us to perform an\nexhaustive search for any short (magnetar-like) or long bursts from\nSSS17a. We build IBIS/ISGRI light-curves in 2 energy ranges: 20-80 keV,\n80-300 keV, on 100 ms, 1 s, 10 s, and 100 s time scales. The\nlightcurves span from 2017-08-18T12:45:10 to 2017-08-23T04:07:47 with\na coverage fraction of 80%. We did not find any deviations from the\nbackground, and set a 3-sigma upper limit on any possible 1-s long\nburst flux of 1.0 Crab (1.4e-8 erg/cm2/s) in 20-80 keV, and 6.8 Crab\n(7.8e-8 erg/cm2/s) in 80-300 keV.\n\nWe also inspected the JEM-X (3-25 keV) light curves at 10 s time\nscale, and did not find any significant fluctuations apart from\nsporadic particle contaminations). The corresponding upper limit in\n3-25 keV is 0.4 Crab (1.3e-8 erg/cm2/s).\n\nAnalysis of the PICsIT spectral-timing data with 100 s time resolution\nin four energy bands spanning 208-2600 keV did not reveal any\nsignificant variability associated with SSS17a during revolutions 1852\nand 1853.\n\nDuring these observation INTEGRAL/IBAS system identified two weak\ntriggers (at 2017-08-22 21:05:59 and 2017-08-22 05:48:21). The\nlocalization of these events is not compatible with SSS17a. We\nconsider these events to be noise associated with moderate solar\nactivity.\n\nUnfortunately, the optical camera on-board INTEGRAL, OMC, was unable to\ndisentangle SSS17a from the host galaxy NGC4993.\n\nWe acknowledge the exceptionally efficient support by the teams at\nESAC and ESOC for the scheduling of this follow-up observation.",
  "circularId": 21672,
  "createdOn": 1503565382000,
  "email": "savchenk@apc.in2p3.fr",
  "subject": "LIGO/Virgo G298048: INTEGRAL pointed follow-up observations",
  "submitter": "Volodymyr Savchenko at APC,Paris  <savchenk@apc.in2p3.fr>",
  "eventId": "LIGO/Virgo G298048"
}