{
"subject": "LIGO/Virgo S200213t: No counterpart candidates in INTEGRAL SPI-ACS prompt observation",
"bibcode": "2020GCN.27050....1R",
"createdOn": 1581578704000,
"circularId": 27050,
"submitter": "James Rodi at IAPS-INAF ",
"email": "james.rodi@inaf.it",
"body": "James Rodi (IAPS-Roma, Italy)\nV. Savchenko, C. Ferrigno (ISDC/UniGE, Switzerland)\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 S200213t (GCN 27042)\n\nAt the time of the event (2020-02-13 04:10:40 UTC, hereafter T0), INTEGRAL\nwas operating in nominal mode. The peak of the event localization\nprobability was at an angle of 139 deg with respect to the spacecraft\npointing axis. This orientation implies strongly suppressed (2.8% of\noptimal) response of ISGRI, somewhat suppressed (60% of optimal) response\nof IBIS/Veto, and strongly suppressed (38% of optimal) response of SPI-ACS.\n\nThe background within +/-300 seconds around the event was rather stable\n(excess variance 1.5).\n\nWe have performed a search for any impulsive events in INTEGRAL SPI-ACS (as\ndescribed in [2]) data.\n\nWe do not detect any significant counterparts and estimate a 3-sigma upper\nlimit on the 75-2000 keV fluence of 4.8e-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) occurring\nat any time in the interval within 300 s around T0. For a typical long GRB\nspectrum (Band function with alpha=-1, beta=-2.5, and Ep=300 keV), the\nderived peak flux upper limit is ~4.6e-07 (1.9e-07) erg/cm^2/s at 1 s (8 s)\ntime scale in 75-2000 keV energy range.\n\nFor the mean reported distance 224.0 Mpc this corresponds to the limit on\nthe total isotropic equivalent energy in 1 s of 2.9e+48 erg for the short\nGRB spectrum and for a long GRB spectrum isotropic equivalent luminosity in\n1 s (8 s) of 2.5e+48 erg/s (1.1e+48 erg/s)\n\nWe report for completeness and in order of FAP, all excesses identified in\nthe search region. We find: 5 likely background excesses:\n\nT-T0 | scale | S/N | luminosity ( x 1e+48 erg/s) | FAP\n-3.11 | 0.3 | 3.5 | 6.47 +/- 1.85 +/- 2.45 | 0.0691\n-3.88 | 0.05 | 4 | 17.7 +/- 4.62 +/- 6.7 | 0.147\n61.7 | 1.7 | 3.3 | 27.7 +/- 7.74 +/- 10.5 | 0.368\n-148 | 1.1 | 3.7 | 36.7 +/- 9.64 +/- 13.9 | 0.676\n254 | 0.75 | 4.1 | 4.88 +/- 1.17 +/- 1.85 | 0.974\n\nNote that FAP estimates (especially at timescales above 2s) may be possibly\nfurther affected by enhanced non-stationary local background noise. This\nlist 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\nteam.\n\n[1] Savchenko et al. 2017, A&A 603, A46\n[2] Savchenko et al. 2012, A&A 541A, 122S"
}