TITLE: GCN CIRCULAR NUMBER: 25232 SUBJECT: IceCube 190730A: one weakly associated counterpart candidates in INTEGRAL SPI-ACS, and IBIS prompt observation DATE: 19/07/31 10:10:41 GMT FROM: Carlo Ferrigno at IAAT/ISDC C. Ferrigno, V. Savchenko (ISDC/UniGE, Switzerland) Maeve Doyle (UCD, Ireland), Alexander Lutovinov (IKI, Moscow, Russia) 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 the INTEGRAL all-sky detectors SPI/ACS (following [1]), IBIS/Veto, and IBIS, we have performed a search for a prompt gamma-ray counterpart of IceCube 190730A, a probable high-energy neutrino (GCN 25225). At the time of the event (2019-07-30 20:50:41 UTC, hereafter T0), INTEGRAL was operating in nominal mode. The most likely event localization was at an angle of 81 deg with respect to the spacecraft pointing axis. This orientation implies strongly suppressed (15% of optimal) response of ISGRI, strongly suppressed (31% of optimal) response of IBIS/Veto, and near-optimal (90% of optimal) response of SPI-ACS. The background within +/-300 seconds around the event was very stable (excess variance 1.1). However, we note the presence of excessive background variations in the hours surrounding the event, increasing the chance of spurious counterpart associations, and complicating the preliminary background estimation reported here. We have performed a search for impulsive events in INTEGRAL SPI-ACS (as described in [2]), IBIS, and IBIS/Veto data. We detect a moderately significant event (S/N 4.7) at 30s time scale at T0+10 s. The peak count rate (30s time scale) of the signal in SPI-ACS is 314 cts/s, which corresponds to 4.7e-8 erg/cm2/s in the 75-2000 keV energy range, assuming coordinates within the localization region and a typical long GRB spectrum (Band function with alpha=-1, beta=-2.5, and Ep=300 keV). This estimate does not account for uncertainties related to the unknown event spectrum, systematic uncertainty on the response (20%), or any dead-time correction. The non-detection of the event in IBIS would be compatible with a source at the location of the IceCube neutrino. We derive a preliminary estimate of the association False Alarm Probability (FAP) at the level of 0.046 (2 sigma), which suggests a likely random coincidence. Further analysis, taking into account accurate FAR measured on the basis of the study of the background during days surrounding the event will be reported elsewhere. Given the high chance of a random coincidence of the above event, we estimate a 3-sigma upper limit on the 75-2000 keV fluence of 1.8e-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 the typical long GRB spectrum used also above, the derived peak flux upper limit is ~1.6e-07 (5.4e-08) erg/cm^2/s at 1 s (8 s) time scale in 75-2000 keV energy range. From now on, we will report all the low-S/N excesses detected by our pipelines with preliminary FAP below unity, which are likely background fluctuations. In addition to the event described above, we find:       scale (s) | T-T0 (s) | S/N | flux ( x 1e-7 erg/cm2/s) |   FAP        0.25     | -6.6     | 3.1 | 4.11 +/-  1.22 +/-   1.1 | 0.433        0.95     |  101     | 3.5 | 2.31 +/- 0.625 +/- 0.618 | 0.785 In this list "flux" is the derived flux assuming a short-GRB typical spectrum with statistical and systematic uncertainties. Note that FAP estimates (especially at timescales above 2s) may be underestimated due to non-stationary local background noise. 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