{
  "bibcode": "2019GCN.25815....1O",
  "body": "Francesca Onori, Antonio Martin-Carrillo\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\nUsing INTEGRAL/SPI-ACS realtime data (following [1]) we have performed\na search for a prompt gamma-ray counterpart of S190923y (GCN 25814).\n\nAt the time of the event (2019-09-23 12:55:59 UTC, hereafter T0),\nINTEGRAL was operating in nominal mode. The peak of the event\nlocalization probability was at an angle of 157 deg with respect to\nthe spacecraft pointing axis. This orientation implies strongly\nsuppressed (3% of optimal) response of ISGRI, somewhat suppressed (62%\nof optimal) response of IBIS/Veto, and somewhat suppresse d (43% of\noptimal) response of SPI-ACS.\n\nThe background within +/-300 seconds around the event was very stable\n(excess variance 1.1).\n\nWe have performed a search for any impulsive events in INTEGRAL SPI-\nACS (as described in [2]) 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 (6.7e-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 tot al isotropic equivalent energy in 1 s of 7.9e+48 erg for\nthe short GRB spectrum and for a long GRB spectrum isotropic\nequivalent luminosity in 1 s (8 s) of 4e+48 erg/s (1.5e+48 erg/s)\n\nWe report for completeness and in order of FAP, all excesses\nidentified in the search region. We find: 6 likely background\nexcesses:\n\nscale | T | S/N | luminosity ( x 1e+49 erg/s) | FAP\n1.7 | -41.9 | 4.4 | 8.61 +/- 2.55 +/- 5.68 | 0.0534\n1.6 | -60.1 | 4.1 | 8.38 +/- 2.63 +/- 5.53 | 0.109\n2.55 | 131 | 3.4 | 5.54 +/- 2.08 +/- 3.66 | 0.424\n1 | 92 | 3.7 | 9.32 +/- 3.32 +/- 6.15 | 0.456\n3.75 | -93.8 | 3 | 3.9 +/- 1.71 +/- 2.58 | 0.581\n0.05 | -2.35 | 3.2 | 3.73 +/- 1.51 +/- 2.46 | 0.635\n\nNote that FAP estimates (especially at timescales above 2s) may be\npossibly further affected by enhanced non-stationary local background\nnoise. This list excludes any excesses for which FAP is close to\nunity.\n\nPart of the probability region was serendipitously observed\nby INTEGRAL FoV instruments (IBIS, JEM-X), analysis is ongoing.\nThere was not ISGRI / IBIS detection at the time of the event, indicating\nabsence\nof strong counterpart in IBIS.\n\nAll results quoted are preliminary.\n\n\nThis circular is an official product of the INTEGRAL Multi-Messenger\nteam.\n\n[1] Savchenko et al. 2017, A&A 603, A46 [2] Savchenko et al. 2012, A&A\n541A, 122S\n-- \nDr. Francesca Onori\nPostdoctoral Researcher\nIAPS, via Fosso del Cavaliere, 100, 00133 - Rome, Italy\ne-mail: francesca.onori@inaf.it\nTel: +39 06 45488128",
  "circularId": 25815,
  "createdOn": 1569248119000,
  "email": "francesca.onori@inaf.it",
  "subject": "LIGO/Virgo S190923y: No counterpart candidates in INTEGRAL SPI-ACS prompt observation",
  "submitter": "Francesca Onori at INAF/IAPS  <francesca.onori@inaf.it>",
  "eventId": "LIGO/Virgo S190923y"
}