{
  "bibcode": "2019GCN.25500....1B",
  "body": "E. Bozzo (ISDC/UniGE, Switzerland), S. Schanne (CEA, France)\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 a \nsearch for a prompt gamma-ray counterpart of S190828j (GCN 25497).\n\nAt the time of the event (2019-08-28 06:34:05 UTC, hereafter T0), \nINTEGRAL was operating in nominal mode. The peak of the event \nlocalization probability was at an angle of 83 deg with respect to the \nspacecraft pointing axis. This orientation implies strongly suppressed \n(11% of optimal) response of ISGRI, strongly suppressed (31% of optimal) \nresponse of IBIS/Veto, and near-optimal (80% of optimal) response of \nSPI-ACS.\n\nThe background within +/-300 seconds around the event was very stable \n(excess variance 1.2).\n\nWe have performed a search for any impulsive events in INTEGRAL SPI-ACS \n(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 2e-07 erg/cm^2 (within the 50% \nprobability containment region of the source localization) for a burst \nlasting less than 1 s with a characteristic short GRB spectrum (an \nexponentially 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 ~1.7e-07 (5.6e-08) \nerg/cm^2/s at 1 s (8 s) time scale in 75-2000 keV energy range.\n\nFor the mean reported distance 2276.0 Mpc this corresponds to the limit \non the total isotropic equivalent energy in 1 s of 1.2e+50 erg for the \nshort GRB spectrum and for a long GRB spectrum isotropic equivalent \nluminosity in 1 s (8 s) of 1.1e+50 erg/s (3.5e+49 erg/s)\n\nWe report for completeness and in order of FAP, all excesses identified \nin the search region. We find 9 background excesses:\n\nscale | T | S/N | luminosity ( x 1e+50 erg/s) | FAP\n5.2 | -276 | 3.9 | 9.22 +/- 3.03 +/- 5.34 | 0.2\n0.55 | -20.1 | 3.6 | 27.9 +/- 9.38 +/- 16.2 | 0.223\n0.1 | -1.25 | 3.1 | 5.75 +/- 2.22 +/- 3.33 | 0.249\n0.2 | 10.7 | 3.5 | 4.58 +/- 1.56 +/- 2.65 | 0.393\n1.6 | 37.3 | 3.1 | 13.9 +/- 5.48 +/- 8.05 | 0.46\n1.4 | -135 | 3.6 | 17.3 +/- 5.86 +/- 10 | 0.547\n0.05 | -7.63 | 3.6 | 9.67 +/- 3.17 +/- 5.6 | 0.564\n0.55 | 63.4 | 3.5 | 27.3 +/- 9.38 +/- 15.8 | 0.807\n0.95 | -60.6 | 3.2 | 19.3 +/- 7.12 +/- 11.2 | 0.83\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 unity.\n\n\n\nAll results quoted are preliminary.\n\nThis circular is an official product of the INTEGRAL Multi-Messenger team.\n\n[1] Savchenko et al. 2017, A&A, 603, A46\n\n[2] Savchenko et al. 2012, A&A, 541A, 122S",
  "circularId": 25500,
  "createdOn": 1566981467000,
  "email": "Enrico.Bozzo@unige.ch",
  "subject": "LIGO/Virgo S190828j: No counterpart candidates in INTEGRAL SPI-ACS prompt observation",
  "submitter": "Enrico Bozzo at ISDC  <Enrico.Bozzo@unige.ch>",
  "eventId": "LIGO/Virgo S190828j"
}