TITLE: GCN CIRCULAR NUMBER: 9867 SUBJECT: GRB 090902B: Fermi LAT detection DATE: 09/09/02 22:48:18 GMT FROM: Hiroyasu Tajima at SLAC Francesco de Palma (Università e INFN Bari), Johan Bregeon (INFN, Pisa) and Hiro Tajima (SLAC) report on behalf of the Fermi LAT team: At 11:05:15 UT on 2 Sep 2009, the Fermi Large Area Telescope (LAT) detected gamma rays from the long GRB 090902B, which was triggered and located by the Fermi Gamma-ray Burst Monitor (GBM) (trigger 273582310/090902462, GCN9866). The angle of the GBM best position (RA, Dec= 264.5, 26.5) with respect to the LAT boresight was 51 degrees at the time of the trigger, which is close the edge of our field of view. The data from the Fermi LAT show a significant increase in the event rate within 1 degree of the GBM location after the GBM trigger that is spatially and temporally correlated with the GBM emission with high significance. More than 200 photons above 100 MeV and more than 30 photons above 1 GeV are observed within 100 seconds. The highest energy photon is a 33.4 GeV event which is observed 82 seconds after the GBM trigger. The best LAT on-ground localization is found to be (RA,Dec=265.00, 27.33) with a 90% containment radius of 0.06 deg (statistical; 68% containment radius: 0.04 deg, preliminary systematic error is less than 0.1 deg) which is consistent with the GBM localization. A Swift TOO request has been issued. Further analysis is ongoing. The point of contact for this burst is Francesco de Palma (francesco.depalma@ba.infn.it) 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. This message can be cited.