TITLE: GCN CIRCULAR NUMBER: 21481 SUBJECT: LIGO/Virgo G297595 : Fermi-LAT search for high-energy gamma-ray counterpart DATE: 17/08/14 19:04:59 GMT FROM: Daniel Kocevski at NASA/MSFC D. Kocevski (NASA/Marshall), N. Omodei (Stanford), F. Longo (University and INFN, Trieste), S. Buson (NASA/GSFC), G.Vianello (Stanford), and J. McEnery (NASA/GSFC) report on behalf of the Fermi-LAT team: We have searched data collected by the Fermi Large Area Telescope (LAT) for possible high-energy (E > 100 MeV) gamma-ray emission in spatial/temporal coincidence with the LIGO/Virgo trigger G297595. At the time of the trigger (T0 = 2017-08-14 10:30:43.529 , 524399448.529 MET), 64% of the LIGO Bayestar probability map was in the LAT field of view, and we reached 100% cumulative coverage within 943 ks after the trigger. We define "instantaneous coverage" as the integral over the region of the LIGO 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 LIGO 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.