TITLE: GCN CIRCULAR NUMBER: 21507 SUBJECT: LIGO/Virgo G298048: INTEGRAL detection of a prompt gamma-ray counterpart DATE: 17/08/17 13:57:47 GMT FROM: Volodymyr Savchenko at APC,Paris V. Savchenko (ISDC, University of Geneva, CH) on behalf of the INTEGRAL group: S. Mereghetti (IASF-Milano, Italy), C. Ferrigno ((ISDC, University of Geneva, CH), E. Kuulkers (ESTEC/ESA, The Netherlands), A. Bazzano (IAPS-Roma, Italy), E. Bozzo, T. J.-L. Courvoisier (ISDC, University of Geneva, CH) S. Brandt (DTU - Denmark) R. Diehl (MPE-Garching, Germany) L. Hanlon (UCD, Ireland) P. Laurent (APC, Saclay/CEA, France) A. Lutovinov (IKI, Russia) J.P. Roques (CESR, France) R. Sunyaev (IKI, Russia) P. Ubertini (IAPS-Roma, Italy) We investigated serendipitous INTEGRAL observations carried out at the time of the LIGO/Virgo burst candidate G298048. The satellite was covering a fraction of the probability of the LIGO-Virgo localization. The best sensitivity depends on the source location. We investigated the SPI-ACS light curves between -30 and +30 s from the trigger time (2017-08-17 12:41:04 UTC, T0) on temporal scales from 0.1 to 100s. In the SPI-ACS data, we detect a short and relatively weak transient with S/N of at T0, with an S/N larger than 3. coincident with the GBM trigger (Connaughton 2017, GCN 21506). Further analysis is ongoing, and will be reported in the coming circulars.