{
"subject": "LIGO/Virgo S200316bj: No counterpart candidates in INTEGRAL SPI-ACS, and IBIS prompt observation",
"bibcode": "2020GCN.27397....1F",
"createdOn": 1584444842000,
"circularId": 27397,
"submitter": "Carlo Ferrigno at IAAT/ISDC ",
"email": "carlo.Ferrigno@unige.ch",
"body": "C. Ferrigno, V. Savchenko (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 combination of INTEGRAL all-sky detectors (following [1]):\nSPI/ACS, IBIS/Veto, and IBIS we have performed a search for a prompt\ngamma-ray counterpart of S200316bj (GCN 27388).\n\nAt the time of the event (2020-03-16 21:57:56 UTC, hereafter T0),\nINTEGRAL was operating in nominal mode. The peak of the event\nlocalization probability was at an angle of 171 deg with respect to\nthe spacecraft pointing axis. This orientation implies strongly\nsuppressed (3.9% of optimal) response of ISGRI, near-optimal (91% of\noptimal) response of IBIS/Veto, and strongly suppressed (34% of\noptimal) response of SPI-ACS.\n\nThe background within +/-300 seconds around the event was very \nstable(excess variance 1.2).\n\nWe have performed a search for any impulsive events in INTEGRAL SPI-\nACS (as described in [2]), IBIS, and IBIS/Veto data.\n\nWe do not detect any significant counterparts and estimate a 3-sigma\nupper limit on the 75-2000 keV fluence of 4.3e-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 ~4.4e-07 (7.8e-08)\nerg/cm^2/s at 1 s (8 s) time scale in 75-2000 keV energy range.\n\nFor the mean reported distance 1222.0 Mpc this corresponds to the\nlimit on the total isotropic equivalent energy in 1 s of 7.6e+49 erg\nfor the short GRB spectrum and for a long GRB spectrum isotropic\nequivalent luminosity in 1 s (8 s) of 3.4e+49 erg/s (1.4e+49 erg/s)\n\nWe report for completeness and in order of FAP, all excesses\nidentified in the search region. We find: 4 likely background\nexcesses:\n\nT-T0 | scale | S/N | luminosity ( x 1e+50 erg/s) | FAP\n-26 | 0.4 | 4.3 | 14.6 +/- 4.42 +/- 9.79 | 0.152\n-111 | 2.25 | 3.4 | 5.17 +/- 1.85 +/- 3.48 | 0.391\n-42.2 | 0.75 | 3.2 | 7.84 +/- 3.21 +/- 5.27 | 0.857\n-50.8 | 0.9 | 3.2 | 6.96 +/- 2.93 +/- 4.68 | 0.891\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\nunity.\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 [2] Savchenko et al. 2012, A&A\n541A, 122S"
}