TITLE: GCN CIRCULAR NUMBER: 27613 SUBJECT: IceCube-200421A: No counterpart candidates in INTEGRAL SPI-ACS and IBIS prompt observation DATE: 20/04/21 10:30:17 GMT FROM: Alexander Lutovinov at Space Research Inst.,IKI Alexander Lutovinov (IKI, Russia),  Enrico Bozzo, V. Savchenko, C. Ferrigno (ISDC/UniGE, Switzerland) J. Rodi (IAPS-Roma, Italy) A. Coleiro (APC, France) S. Mereghetti (INAF IASF-Milano, Italy) on behalf of the INTEGRAL multi-messenger collaboration: https://www.astro.unige.ch/cdci/integral-multimessenger-collaboration Using combination of INTEGRAL all-sky detectors (following [1]): SPI/ACS, IBIS/Veto, and IBIS we have performed a search for a prompt gamma-ray counterpart of unknown (GCN 27612). At the time of the event (2020-04-21 00:35:24 UTC, hereafter T0), INTEGRAL was operating in nominal mode. The peak of the event localization probability was at an angle of 162 deg with respect to the spacecraft pointing axis. This orientation implies strongly suppressed (3.7% of optimal) response of ISGRI, near-optimal (85% of optimal) response of IBIS/Veto, and strongly suppressed (38% of optimal) response of SPI-ACS. The background within +/-300 seconds around the event was rather stable (excess variance 1.3). We have performed a search for any impulsive events in INTEGRAL SPI- ACS (as described in [2]), IBIS, and IBIS/Veto data. We do not detect any significant counterparts and estimate a 3-sigma upper limit on the 75-2000 keV fluence of 4.9e-07 erg/cm^2 (within the 50% probability containment region of the source localization) for a burst lasting less than 1 s with a characteristic short GRB spectrum (an exponentially cut off power law with alpha=-0.5 and Ep=600 keV) occurring at any time in the interval within 300 s around T0. For a typical long GRB spectrum (Band function with alpha=-1, beta=-2.5, and Ep=300 keV), the derived peak flux upper limit is ~5e-07 (9.2e-08) erg/cm^2/s at 1 s (8 s) time scale in 75-2000 keV energy range. We report for completeness and in order of FAP, all excesses identified in the search region. We find: 2 possibly associated excesses: T-T0 | scale | S/N | flux ( x 1e-06 erg/cm2/s) | FAP 3.07 | 1.15 | 3.6 | 0.553 +/- 0.152 +/- 0.186 | 0.0163 40 | 9.5 | 3.5 | 2.09 +/- 0.526 +/- 0.703 | 0.033 2 likely background excesses: T-T0 | scale | S/N | flux ( x 1e-06 erg/cm2/s) | FAP -36.6 | 1.5 | 3.3 | 0.433 +/- 0.133 +/- 0.146 | 0.307 -119 | 0.35 | 4.6 | 1.25 +/- 0.277 +/- 0.419 | 0.668 All results quoted are preliminary. This circular is an official product of the INTEGRAL Multi-Messenger team. [1] Savchenko et al. 2017, A&A 603, A46 [2] Savchenko et al. 2012, A&A 541A, 122S