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.