{
"subject": "IceCube 190730A: one weakly associated counterpart candidates in INTEGRAL SPI-ACS, and IBIS prompt observation",
"bibcode": "2019GCN.25232....1F",
"createdOn": 1564567841000,
"circularId": 25232,
"submitter": "Carlo Ferrigno at IAAT/ISDC ",
"email": "carlo.Ferrigno@unige.ch",
"body": "C. Ferrigno, V. Savchenko (ISDC/UniGE, Switzerland)\nMaeve Doyle (UCD, Ireland), Alexander Lutovinov (IKI, Moscow, Russia)\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 the INTEGRAL all-sky detectors\nSPI/ACS (following [1]), IBIS/Veto, and IBIS, we have performed a search \nfor a prompt\ngamma-ray counterpart of IceCube 190730A, a probable high-energy \nneutrino (GCN 25225).\n\nAt the time of the event (2019-07-30 20:50:41 UTC, hereafter T0),\nINTEGRAL was operating in nominal mode. The most likely event\nlocalization was at an angle of 81 deg with respect to the\nspacecraft pointing axis. This orientation implies strongly suppressed\n(15% of optimal) response of ISGRI, strongly suppressed (31% of\noptimal) response of IBIS/Veto, and near-optimal (90% of optimal)\nresponse of SPI-ACS.\n\nThe background within +/-300 seconds around the event was very stable\n(excess variance 1.1). However, we note the presence of excessive background\nvariations in the hours surrounding the event, increasing the chance of\nspurious counterpart associations, and complicating the preliminary \nbackground estimation reported here.\n\nWe have performed a search for impulsive events in INTEGRAL SPI-ACS\n(as described in [2]), IBIS, and IBIS/Veto data. We detect a moderately\nsignificant event (S/N 4.7) at 30s time scale at T0+10 s.\nThe peak count rate (30s time scale) of the signal in SPI-ACS is 314 cts/s,\nwhich corresponds to 4.7e-8 erg/cm2/s in the 75-2000 keV energy range,\nassuming coordinates within the localization region and a typical\nlong GRB spectrum (Band function with alpha=-1, beta=-2.5, and Ep=300 keV).\nThis estimate does not account for uncertainties related to the unknown \nevent spectrum,\nsystematic uncertainty on the response (20%), or any dead-time correction.\nThe non-detection of the event in IBIS would be compatible with a source\nat the location of the IceCube neutrino.\nWe derive a preliminary estimate of the association False Alarm \nProbability (FAP)\nat the level of 0.046 (2 sigma), which suggests a likely random \ncoincidence.\nFurther analysis, taking into account accurate FAR measured on the basis \nof the study of the background during days surrounding the event will be \nreported elsewhere.\n\n\nGiven the high chance of a random coincidence of the above event,\nwe estimate a 3-sigma upper limit on the 75-2000 keV\nfluence of 1.8e-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 the typical long GRB spectrum used \nalso above,\nthe derived peak flux upper limit is ~1.6e-07 (5.4e-08) erg/cm^2/s at 1 \ns (8 s) time\nscale in 75-2000 keV energy range.\n\n From now on, we will report all the low-S/N excesses detected by our \npipelines\nwith preliminary FAP below unity, which are likely background fluctuations.\nIn addition to the event described above, we find:\n\n ���� ���� scale (s) | T-T0 (s) | S/N | flux ( x 1e-7 erg/cm2/s) |���� FAP\n ������������ 0.25�������� | -6.6�������� | 3.1 | 4.11 +/-�� 1.22 +/-���� 1.1 | 0.433\n ������������ 0.95�������� |�� 101�������� | 3.5 | 2.31 +/- 0.625 +/- 0.618 | 0.785\n\nIn this list \"flux\" is the derived flux assuming a short-GRB typical \nspectrum\nwith statistical and systematic uncertainties.\nNote that FAP estimates (especially at timescales above 2s) may be \nunderestimated\ndue to non-stationary local background noise.\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[2] Savchenko et al. 2012, A&A 541A, 122S"
}