TITLE: GCN CIRCULAR NUMBER: 18813 SUBJECT: LIGO/Virgo G211117: Fermi/LAT observations DATE: 16/01/04 06:56:39 GMT FROM: Giacomo Vianello at Stanford U/Fermi LAT 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.