TITLE: GCN CIRCULAR NUMBER: 15587 SUBJECT: GRB 131209A: Fermi-LAT detection of a burst DATE: 13/12/10 02:06:01 GMT FROM: Giacomo Vianello at SLAC G.Vianello (Stanford), N.Omodei (Stanford), report on behalf of the Fermi-LAT team: At 13:07:56.97on December 9, 2013, Fermi LAT detected a faint high energy signal from GRB131209A, which was also detected by Fermi-GBM (trigger 408287279/131209547). The data from the Fermi LAT show a significant increase in the event rate within 10 degree of the GBM location after the GBM trigger that is spatially and temporally correlated with the GBM emission. Although the detection is slightly above the 5 sigma level, there are only 4 photons likely associated with this GRB in the first 200 s after the trigger. The localization has therefore a large statistical error. The best LAT on-ground location is found to be RA, DEC 136.5, -33.2 (J2000) with an error radius of 0.9 deg (68% containment, statistical error only), this was 20 deg from the LAT boresight at the time of the trigger. The Fermi LAT point of contact for this burst is Giacomo Vianello ( giacomov@stanford.edu). 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.