TITLE: GCN CIRCULAR NUMBER: 21695 SUBJECT: LIGO/Virgo G297595: INTEGRAL pointed follow-up observations DATE: 17/08/25 14:33:57 GMT FROM: Volodymyr Savchenko at APC,Paris V. Savchenko (ISDC, University of Geneva, CH) on behalf of the INTEGRAL group: C. Ferrigno, E. Bozzo ((ISDC, University of Geneva, CH), E. Kuulkers (ESTEC/ESA, The Netherlands), S. Mereghetti (IASF-Milano, Italy), T. J.-L. Courvoisier (ISDC, University of Geneva, CH) J. Chenevez, S. Brandt (DTU - Denmark) R. Diehl (MPE-Garching, Germany) L. Hanlon (UCD, Ireland) P. Laurent (APC, Saclay/CEA, France), D. Gotz (DRF/Irfu/DAp Saclay/CEA) J.P. Roques, E. Jourdain (IRAP, France) P. Ubertini, A. Bazzano, J. Rodi (IAPS-Roma, Italy) A. Lutovinov, R. Sunyaev (IKI, Russia) INTEGRAL is an observatory with multiple instruments: a gamma-ray spectrometer (20 keV -4 MeV, SPI), an imager (15 keV - 2 MeV, IBIS), an X-ray monitor (3-25 keV, JEM-X), and an optical monitor (V band, OMC). Our group requested and obtained pointed follow-up observations of the LIGO/Virgo candidate BBH merger G297595 (GCN 21474). The INTEGRAL follow-up observation was centered on RA=41.07 Dec=-45.49, close to the peak of the LIGO/Virgo localization probability, taking into account observational constrains. This observation spanned from 2017-08-16 at 10:04 to 2017-08-17 at 18:19 (starting about 47 hours after the LIGO/Virgo event), with a maximum on-source time of 97.5 ks (depending on the instrument). IBIS and SPI observed more than 92% of the of LIGO/Virgo localization in the combined observation mosaic. JEM-X covered about 79%, owing to its smaller Field of View. INTEGRAL provides the most stringent constraint on any possible emission associated with G297595, above 80 keV. We searched IBIS/ISGRI and JEM-X data for new point sources in the whole 90% LIGO/Virgo localization region, and did not find any. We set the following 3-sigma upper limits for the average flux: JEM-X: 3-10 keV: 2.0 mCrab (3.2e-11 erg/cm2/s ) 10-25 keV: 1.0 mCrab (1.1e-11 erg/cm2/s ) ISGRI: 20-80 keV: 3.3 mCrab (4.9e-11 erg/cm2/s) 80-300 keV: 13.1 mCrab (1.5e-10 erg/cm2/s) In the case of ISGRI (JEM-X), 82% (59%) of the of LIGO/Virgo localization is covered with sensitivity no more than factor two worse than the best. During these observation online INTEGRAL/IBAS system identified several weak triggers. After offline inspection, we consider these triggers unrelated noise. INTEGRAL/IBAS online search in the SPI-ACS identified a bright GRB170816A on 2017-08-16 at 14:22:58. The location of this GRB is inconsistent with the LIGO/Virgo 90% localization (GCN 21504, 21517). Finally, the BNS merger G298048 (GCN 21509, 21513) candidate counterpart (GRB 170817A, GCN 21506, 21520) was detected in the INTEGRAL data during this observation, as reported in GCN 21507. We have also inspected PICsIT spectral-timing data (200 - 2600 keV) and did not find any evidence for significant variability. Further analysis is ongoing. We acknowledge the essential support by the teams at ESAC and ESOC for the scheduling of this follow-up observation.