{
"subject": "LIGO/Virgo S190923y: INTEGRAL IBIS coded-masked imaging observations of part of the localization area and further all-sky upper limits",
"bibcode": "2019GCN.25825....1M",
"createdOn": 1569275049000,
"circularId": 25825,
"submitter": "Antonio Martin-Carrillo at UCD,Space Science Group ",
"email": "antonio.martin-carrillo@ucd.ie",
"body": "Antonio Martin-Carrillo (UCD), Francesca Onori, \nV. Savchenko, C. Ferrigno (ISDC/UniGE, Switzerland)\nJ. Rodi (IAPS-Roma, Italy)\nA. Coleiro (APC, France)\nS. Mereghetti (INAF IASF-Milano, Italy)\n\non behalf of the INTEGRAL multi-messenger collaboration:\nhttps://www.astro.unige.ch/cdci/integral-multimessenger-collaboration\n\nAt the time of the event S190923y (2019-09-23 12:55:59 UTC, GCN 25814) and based on the initial localization map, 8% of the LIGO/Virgo GW localization was within the field of view of IBIS. The background within +/-300 seconds around the event was very stable (excess variance 1.1).\n\nInitial analysis of the pointed observations of IBIS do not reveal any relevant counterparts at this point. 3-sigma upper limits of about 5e-10erg/cm2/s (28-40 keV energy range) in single pointings of about 30 min at ~T0+5.5h have been found in areas at the edge of the 90% LIGO/Virgo contour. \n\nINTEGRAL will continue to serendipitously observe the localization area\nof S190923y over the nex few hours. Any relevant candidates will be reported separately.\n\nWe have included this new data to the initial results presented in Onori et al (GCN 25815) to search for any impulsive events in INTEGRAL SPI-\nACS (as described in [1]), IBIS, and IBIS/Veto data.\n\nWe do not detect any significant counterparts and estimate a 3-sigma\nupper limit on the 75-2000 keV fluence of 3.4e-07 erg/cm^2 (within the\n50% probability containment region of the source localization) for a\nburst lasting less than 1 s with a characteristic short GRB spectrum\n(an exponentially cut off power law with alpha=-0.5 and Ep=600 keV)\noccurring at any time in the interval within 300 s around T0. For a\ntypical long GRB spectrum (Band function with alpha=-1, beta=-2.5, and\nEp=300 keV), the derived peak flux upper limit is ~3.4e-07 (3.7e-08)\nerg/cm^2/s at 1 s (8 s) time scale in 75-2000 keV energy range.\n\nFor the mean reported distance 438.0 Mpc this corresponds to the limit\non the total isotropic equivalent energy in 1 s of 7.8e+48 erg for\nthe short GRB spectrum and for a long GRB spectrum isotropic\nequivalent luminosity in 1 s (8 s) of 2.6e+48 erg/s (8.6e+47 erg/s)\n\nThese upper limits take into account that the peak of the event\nlocalization probability was at an angle of 158 deg with respect to\nthe spacecraft pointing axis at the time of the trigger. \nThis orientation implies strongly\nsuppressed (3.2% of optimal) response of ISGRI, somewhat suppressed\n(62% of optimal) response of IBIS/Veto, and somewhat suppressed (43%\nof optimal) response of SPI-ACS.\n\n\nAll results quoted are preliminary.\nThis circular is an official product of the INTEGRAL Multi-Messenger\nteam.\n\n[1] Savchenko et al. 2012, A&A 541A, 122S"
}