{
"subject": "Fermi GBM-190816: Location-dependent upper limits from INTEGRAL/SPI-ACS prompt observation",
"bibcode": "2019GCN.25407....1S",
"createdOn": 1566292139000,
"circularId": 25407,
"submitter": "Volodymyr Savchenko at ISDC,U of Geneve ",
"email": "savchenk@in2p3.fr",
"body": "V. Savchenko, C. Ferrigno (ISDC/UniGE, Switzerland)\nS. Molkov (IKI, 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 INTEGRAL/SPI-ACS realtime data (following [1]) we have performed\na search for a prompt gamma-ray counterpart of GBM-190816 (GCN 25406).\nAt the time of the event (2019-08-16 21:22:14.6 UTC, hereafter T0),\nINTEGRAL was operating in nominal mode. The peak of the event\nlocalization probability was at an angle of 98 deg with respect to the\nspacecraft pointing axis. This orientation implies strongly suppressed\n(7.7% of optimal) response of ISGRI, strongly suppressed (22% of\noptimal) response of IBIS/Veto, and near-optimal (87% of optimal)\nresponse of SPI-ACS. The background within +/-300 seconds around the\nevent was very stable(excess variance 1.1).\n\nWe have performed a search for impulsive events in INTEGRAL SPI-\nACS data, as described in [2].\n\nWe do not detect any significant counterparts and estimate a 3-sigma\nupper limit on the 75-2000 keV fluence of 1.8e-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 ~1.5e-07 (5.5e-08)\nerg/cm^2/s at 1 s (8 s) time scale in 75-2000 keV energy range.\n\nFor the mean reported distance 362 Mpc this corresponds to the limit\non the total isotropic equivalent energy in 1 s of 2.8e+48 erg for the\nshort GRB spectrum and for a long GRB spectrum isotropic equivalent\nluminosity in 1 s (8 s) of 2.4e+48 erg/s (8.6e+47 erg/s)\n\nSince the GW localization region includes regions with particularly large\nrange of SPI-ACS sensitivities, the upper limit from SPI-ACS is very\nlocation-dependent.\n\nWe find 10 excesses in the search region, reported below in order\nof FAP. The excesses are likely due to background noise.\n\nscale���� | T�������� | S/N | luminosity ( x 1e+48 erg/s)������ | FAP\n0.45������ | 1.73�� | 3���� |�������� 13.6 +/- 6.57���� +/- 13.8���� | 0.0917\n0.1�������� | 0.901 | 3.1 |�������� 29.1 +/- 14.1���� +/- 29.5���� | 0.171\n0.35������ | 12.9�� | 3.7 |�������� 18.6 +/- 7.47���� +/- 18.9���� | 0.191\n0.45������ | 15.9�� | 3.5 |�������� 15.5 +/- 6.58���� +/- 15.7���� | 0.25 ��\n1.6�������� | -126�� | 3.8 |�������� 9.12 +/- 3.48���� +/- 9.25���� | 0.344\n4.3�������� | 197���� | 3.4 |�������� 5.27 +/- 2.12���� +/- 5.35���� | 0.411\n0.15������ | -5.32 | 3.3 |�������� 25.4 +/- 11.5���� +/- 25.7���� | 0.421\n0.2�������� | -8.25 | 3.2 |�������� 21.2 +/- 9.9������ +/- 21.6���� | 0.625\n0.35������ | 40.7�� | 3.5 |�������� 17.7 +/- 7.47���� +/- 18�������� | 0.789\n0.05������ | 231���� | 8.6 |�������� 11.9 +/- 2.08���� +/- 12.1���� | 0.819\n\nWhere uncertainties are statistical and systematic. Systematic\nuncertainty includesdependency on the unknown location and\nassumed 20% systematics in the response.\n\nFor any given fluence measured by Fermi/GBM, INTEGRAL observation\ncan constrainthe event location. In particular, the GW localization lobe\nnear RA=12h corresponds to considerably less constraining upper limit,\ncorresponding to the directions through the bottomof the spacecraft.\nHence INTEGRAL non-detection suggests that a source in the GW localization\nlobe near RA=12h of is more likely compatible with the possible GBM\ndetection:\n\nhttps://doi.org/10.5281/zenodo.3372187\n\nHowever we caution that this conclusion depends on unknown event spectrum\nand fluence.\n\nAll results quoted are preliminary.\n\nThis circular is an official product of the INTEGRAL Multi-Messenger team."
}