{
  "bibcode": "2019GCN.25190....1D",
  "body": "Maeve Doyle (UCD, Ireland), Alexander Lutovinov (IKI, Moscow)\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 S190728q (GCN 25187).\n\nAt the time of the event (2019-07-28 06:45:10 UTC, hereafter T0),\nINTEGRAL was operating in nominal mode. The peak of the event\nlocalization probability was at an angle of 91 deg with respect to the\nspacecraft pointing axis. This orientation implies strongly suppressed\n(5.3% of optimal) response of ISGRI, strongly suppressed (13% of\noptimal) response of IBIS/Veto, and somewhat suppressed (58% of\noptimal) response of SPI-ACS.\n\nThe background within +/-300 seconds around the event was rather\nstable (excess variance 1.2).\n\nWe have performed a search for any impulsive events in INTEGRAL SPI-\nACS (as described in [2]) data.\n\nWe detect a marginal event (S/N 5.22, local FAP\n3.27 equivalent sigma) at 0.05s time scale at T0+201.01. Peak count\nrate of the signal in SPI-ACS is 9629 cts/s, which corresponds to\n2.03e-06 to 2.39e-06 erg/cm2/s depending on the location within the\n50% LIGO/Virgo Event localization region and assuming a typical short GRB\nspectrum. This estimate does not explore uncertainty related to the\nunknown event spectrum, systematic uncertainty on the response of 20%,\nor any dead-time correction. For the mean distance to the source of\n795.0 Mpc this corresponds to the isotropic-equivalent luminosity\nbetween 1.53e+50 to 1.8e+50 erg/s. We derive a preliminary estimate of\nthe associated FAP higher than 0.5 (less than 0.67 sigma). This\ntentatively indicates a random coincidence. Further analysis, taking\ninto account accurate FAR measured on the basis of the study of the\nbackground during days surrounding the event will be reported in\nforthcoming circulars.\n\nOtherwise, we estimate a 3-sigma upper limit on the 75-2000 keV\nfluence of 2.6e-07 erg/cm^2 (within the 50% probability containment\nregion of the source localization) for a burst lasting less than 1 s\nwith a characteristic short GRB spectrum (an exponentially cut off\npower law with alpha=-0.5 and Ep=600 keV) occurring at any time in the\ninterval within 300 s around T0. For a typical long GRB spectrum (Band\nfunction with alpha=-1, beta=-2.5, and Ep=300 keV), the derived peak\nflux upper limit is ~2.1e-07 (7.9e-08) erg/cm^2/s at 1 s (8 s) time\nscale in 75-2000 keV energy range.\n\nIn this case, For the mean reported distance 795.0 Mpc this corresponds to the limit\non the total isotropic equivalent energy in 1 s of 1.9e+49 erg for the\nshort GRB spectrum and for a long GRB spectrum the isotropic equivalent\nluminosity can be estimated in 1 s (8 s) as 1.6e+49 erg/s (6e+48 erg/s).\n\nAll results quoted are preliminary.\n\nThis circular is an official product of the INTEGRAL Multi-Messenger\nteam.\n\n[1] Savchenko et al. 2017, A&A 603, A46 \n[2] Savchenko et al. 2012, A&A 541A, 122S",
  "circularId": 25190,
  "createdOn": 1564306387000,
  "email": "maeve.doyle.1@ucdconnect.ie",
  "subject": "LIGO/Virgo S190728q: No counterpart candidates in INTEGRAL SPI-ACS prompt observation",
  "submitter": "Maeve Doyle at U College Dublin, Ireland  <maeve.doyle.1@ucdconnect.ie>",
  "eventId": "LIGO/Virgo S190728q"
}