GCN Circular 20777
G. Vianello (Stanford), N.Omodei (Stanford), Daniel Kocevski (NASA/MSFC) and Sara Buson (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 G275697. Fermi-LAT had an instantaneous coverage of ~20% at the time of the trigger (T0 = 2017-02-27 18:57:31.375 UTC), and reached 100% cumulative coverage within ~7 ks. 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. Energy flux upper bounds between 100 MeV and 100 GeV for this search vary between 3e-10 ��� 3e-9 [erg/cm^2/s]. 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.