{
"subject": "LIGO/Virgo G275404 and AGL J1914+1043: INTEGRAL follow-up",
"bibcode": "2017GCN.20834....1S",
"createdOn": 1488926333000,
"circularId": 20834,
"submitter": "Volodymyr Savchenko at APC,Paris ",
"email": "savchenk@apc.in2p3.fr",
"body": "V. Savchenko (ISDC, University of Geneva, CH)\non behalf of the INTEGRAL group:\nC. Ferrigno ((ISDC, University of Geneva, CH),\nS. Mereghetti (IASF-Milano, Italy),\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\n\nINTEGRAL performed a target-of-opportunity (ToO) observation\ncontaining the peak of the LIGO localization probability of G275404\n(Sachdev et al 2017, GCN 20738) and its possible gamma-ray counterpart\nAGL J1914+1043 (Tavani et al 2017, GCN 20754). In total 56% of the\nLIGO probability and the whole probable localization region of AGL\nJ1914+1043 were observed in the field of view (FoV) of the INTEGRAL\ninstruments.\n\nThe observation containing the peak localization probability of\nG275404 peak (RA= 299.1 Dec=49.3), started 81.5 hours after the\nG275404 trigger time (2017-02-25 18:30:21.4 UTC , T0 hereafter) from\n2017-03-01 04:09:58 UTC to 2017-03-02 05:45:58 UTC, corresponding to\nan on-target time of 85.5 ks. We covered in total 40% of LIGO\nlocalization probability with INTEGRAL/IBIS FoV. Every single\nhour-long spacecraft pointing contained about 30% of the LIGO\nlocalization probability.\n\nThe observation of AGL J1914+1043 started at T0+107.5 hours and\nspanned from 2017-03-02 05:57:54 UTC to 2017-03-03 07:03:05 UTC, with\na total on-target time of 86.5 ks and including an extended region\nwithin a distance of about 15 degrees from the target, securely\nencompassing the region of probable localization reported by AGILE (4\ndeg 68% containment + 1 deg systematic error). This observation\nincludes 16% of G275404 localization in INTEGRAL/IBIS FoV and every\nsingle hour-long instrument pointing contained about 13% of the LIGO\nlocalization probability.\n\nAdditionally, by chance, INTEGRAL observed a non-negligible fraction\nof the G275404 probability before the start of the dedicated\nToO. Despite limited coverage, these observations are useful, since\nthey were performed during the LIGO trigger and as well as immediately\nbefore and after. The observation of the Galactic Bulge region from\n2017-02-26T12:22:54 to 2017-02-26T16:03:52.396 collected 12.5ks of\ndata covering 1.5% of LIGO probability, complementary to that of the\nToO observation. The observation of the Norma Region between\n2017-02-27T07:13:58.431 and 2017-02-28T01:48:14.473 collected 61ks of\ndata covering additionally 2% of the LIGO probability.\n\nWe investigated the data collected by INTEGRAL IBIS/ISGRI and\nJEM-X. We did not find any new significant sources in the 90%\nlocalization region of G275404.\n\nIn INTEGRAL/ISGRI observation of AGL J1914+1043 data between 25 and 80\nkeV we have found a weak excess with an SNR of 4.3 at RA=292.27\nDec=8.14 (radius of 5 arcmin, 90% containment), 4.6 deg from the\ncenter of AGILE localization (RA=288.43 deg, DEC=10.72 deg, and error\nradius R = 4 deg at 68% confidence + 1 deg systematic error). We have\nsplit the observation in two periods of equal duration, and found that\nthis excess is not detected with SNR more than 4 in any of them, hence\nrevealing no sign of evolution. If real, the excess would correspond\nto a source with an average flux of 5.1+/-1.2 mCrab (5.1+-1.2e-11\nerg/cm2/s) in the 25-80 keV band and 3.5+/-1.1 mCrab (2.9+-0.9e-11\nerg/cm2/s) in 25-40 keV band. While this possible source is located in\na region frequently observed by INTEGRAL (for a total of 14Ms between\n2003 and 2017), no possible detection was previously reported at its\nposition.\n\nWe estimate a probability of this excess happening randomly within the\n5 degree radius of the AGILE localization to 3.5% or a significance of\n2.1 sigma.\n\nWe derived an upper limit on the flux of a new source at the peak of\nthe LIGO localization probability of 6 mCrab (1.9e-10 erg/cm2/s) in\nthe 3-35 keV band, 3.6 mCrab (3.6e-11 erg/cm2/s) in the 25-80 keV\nband, and 7 mCrab (8.2x10-11 erg/cm2/s) in the 80-200 keV band. The\nupper limit depends on the source position in the field of view. About\n40% of G275404 is observed with the sensitivity of down to 10 mCrab or\nbetter.\n\nThe localization region of another LIGO event, G275697 (Siellez et al\n2017, GCN 20763), was in the FoV of the INTEGRAL instruments, with the\n30% of the LIGO localization observed by IBIS/ISGRI at any time from\nthe LIGO trigger time to 3.5 days after. At the moment of the LIGO\ntrigger as well as from -0.5 days to 0.3 days around it up to 8% of\nthe probability was in the ISGRI FoV, while at any other moment until\n3.5 days after the trigger up to 15% of the probability was in the\nFoV.\n\nWe note that omni-directional INTEGRAL/SPI-ACS observations around the\nG275404 and G275697 triggers are reported in LIGO/Virgo Circulars\n20755 and GCN 20768."
}