{
  "bibcode": "2019GCN.25309....1S",
  "body": "V. 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\n\nUsing INTEGRAL/SPI-ACS realtime data, and following [1], we have performed\na search for prompt gamma-ray counterparts of HAWC-190806A (GCN 25284).\n\nAt the time of the event (2019-08-06 13:20:48 UTC, hereafter T0),\nINTEGRAL was operating in nominal mode. The event localization was at an\nangle of 33 deg with respect to thespacecraft pointing axis.\nThis orientation implies a strongly suppressed(17% of optimal)\nresponse of ISGRI, a strongly suppressed (31% ofoptimal) response of\nIBIS/Veto, and a near-optimal (75% of optimal)response of SPI-ACS.\nThis orientation implies a favorableresponse of IBIS/PICsIT.\n\nThebackground within +/-300 seconds around�� the event was ratherstable\n(excess variance 1.3, slightly higher than usual).\n\nWe have performed a search for any impulsive events in INTEGRAL SPI-ACS\n(as described in [2]) data. We detect a marginal event (S/N 3.3) at a 3.5s\ntime scale atT0-1.8s. The peak count rate of the signal in SPI-ACS is\n713 cts/s,\nwhich corresponds to a flux between 1.2e-07 and 1.7e-07 erg/cm2/s,\ndepending on thelocation within the source localization region, and\nassuming a typical short GRB spectrum (an exponentially cut offpower law\nwith\nalpha=-0.5 and Ep=600 keV). This estimate does not take into account\nthe uncertaintyrelated to the unknown event spectrum, the 20% systematic\nuncertainty on theresponse, or any dead-time correction. We derive\npreliminary\nestimate of the association FAP at the level of 0.011 (2.3 sigma).\nThis tentatively indicates a random association.\n\nFurther analysis, taking into account accurate FAR measured on\nthe basis of the study ofthe background during days surrounding\nthe event might be reported in aforthcoming circulars.\n\nIn the IBIS/PICsIT analysis, we do not detect any relevant signal,\ndespite an\norientation favorable for this instrument. This disfavours a cosmic origin\nof the observed SPI-ACS excess.\n\nOtherwise, we estimate a 3-sigma upper limit on the 75-2000 keV\nfluence of 2e-07 erg/cm^2 for a burst lasting less than 1 s\nwith a characteristic short GRB spectrum�� 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 ~1.7e-07 (6.9e-08) erg/cm^2/s at 1 s (8 s) time\nscale in 75-2000 keV energy range.\n\nIn addition, we identify the following low-S/N excesses,\nwhich likely belong to thebackground:\n\nscale | T�������� | S/N | flux ( x 1e-7 erg/cm2/s) | FAP\n2.9���� | -135�� | 3.8 | 1.9 �� 0.5 �� 0.8������������������ | 0.2\n2.7���� | -238�� | 4.2 | 2.1 �� 0.5 �� 0.8������������������ | 0.231\n0.1���� | -9.26 | 4.2 | 10.6 �� 2.7 �� 4.4���������������� | 0.248\n0.8���� | 92.7�� | 4.1 | 3.6 �� 0.9 �� 1.5������������������ | 0.341\n0.5���� | -113�� | 3.9 | 4.5 �� 1.2 �� 1.8 �� �� �� ���� | 0.786\n1.1���� | -275�� | 3.9 | 3.0 �� 0.8 �� 1.2������������������ | 0.896\n\nNote that FAP estimates (especially at timescales above 2s) may be\nfurther affected by possibly enhanced non-stationary local background\nnoise.\n\nThis list excludes any excesses for which FAP is close to unity.\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": 25309,
  "createdOn": 1565390652000,
  "email": "savchenk@in2p3.fr",
  "subject": "HAWC-190806A: upper limits from INTEGRAL SPI-ACS and IBIS prompt observation",
  "submitter": "Volodymyr Savchenko at ISDC,U of Geneve  <savchenk@in2p3.fr>",
  "eventId": "HAWC-190806A"
}