TITLE: GCN CIRCULAR NUMBER: 21710 SUBJECT: LIGO/Virgo G299232 : Fermi-LAT search for high-energy gamma-ray counterpart DATE: 17/08/26 02:53:20 GMT FROM: Daniel Kocevski at NASA/MSFC D. Kocevski (NASA/Marshal), G. Vianello (Stanford), N. Omodei (Stanford), S. Buson (NASA/GSFC), N. Di Lalla (Univ. Pisa & INFN Pisa), and M. Razzano (Univ. Pisa & INFN Pisa) report on behalf of the Fermi-LAT team: We searched data collected by the Fermi Large Area Telescope (LAT) for a possible high-energy (E > 100 MeV) gamma-ray emission in spatial/temporal coincidence with the LIGO/Virgo trigger G299232 (GCN 21693). At the time of the trigger (T0 = 2017-08-25 13:13:37.977 UTC, 525359622.977 MET), 40% of the LIGO/Virgo Bayestar probability map based on L1, H1, and V1 observations was in the LAT field of view, and we reached 100% cumulative coverage within ~5400 s after the trigger. We define "instantaneous coverage" as the integral over the region of the probability map that is within the LAT field of view at a given time, and "cumulative coverage" as the integral of the instantaneous coverage over time. We performed a search for a transient counterpart within the 90% contour of the probability map in the time window from T0 to T0 + 10 ks, and no significant new sources are found. We also performed a search which adapted the time interval of the analysis to the exposure of each region of the sky. No significant candidate counterpart was found. The Fermi-LAT point of contact for this event is Daniel Kocevski (daniel.kocevski@nasa.gov) The Fermi-LAT is a pair conversion telescope designed to cover the energy band from 20 MeV to greater than 300 GeV. It is the product of an international collaboration between NASA and DOE in the U.S. and many scientific institutions across France, Italy, Japan and Sweden.