GCN Circular 20374
Giacomo Vianello (Stanford), Daniel Kocevski (NASA/MSFC), Francesco Longo (Trieste University and INFN/Trieste), Julie McEnery (NASA/GSFC), Jeremy S. Perkins (NASA/GSFC) and Judy Racusin (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 G268556. Fermi/LAT had an instantaneous coverage of ~55% at the time of the trigger (T0 = 2017-01-04 10:11:59 UTC), and reached 100% cumulative coverage within 5 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 Bayestar map on the time window from T0 to T0 + 10 ks and found no significant excess. 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.