GCN Circular 18813

G. Vianello (Stanford), M. Razzano (Univ. of Pisa), N. Omodei (Stanford),
J. Racusin (NASA/GSFC), J. McEnery, (NASA/GSFC), M. Briggs (UAH), E. Burns
(UAH), V. Connaughton (USRA), A. Goldstein (NASA/MSFC), P. Jenke (UAH), C.
Wilson-Hodge (NASA/MSFC), B. Zhang (UAH)


We report on the search for a gamma-ray counterpart for the LIGO/VIRGO
candidate G211117 in the data of the Fermi Large Area Telescope. Our search
covered the regions of the LIGO/VIRGO "Bayestar" sky map having a
probability greater than 90%.

We performed a search for a gamma-ray counterpart above 100 MeV on two time
intervals: a) from -100 s to 1000 s after the GW trigger, and b) from -100
s to 10000 s after the trigger. Time scale "a" is the typical time scale
for a search for short GRBs, while the second time scale is more typical
for long GRBs.

At the time of the GW trigger Fermi was operating in normal survey mode.
During the time interval "a" around half of the North region and almost all
the South region were inside the LAT FoV at some point. During the time
interval "b" both regions were covered in their entirety. A counts map of
the full sky relative to this second interval can be seen at:

https://gracedb.ligo.org/apiweb/events/G211117/files/fermi_sky_map.png

We found no significant excess above a significance of 3 sigma post-trial.

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.