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GCN Circular 9985

GRB 091003A: Fermi LAT detection
2009-10-03T21:46:38Z (15 years ago)
Julie McEnery at UMBC/GSFC <>
Julie McEnery (NASA/GSFC), Jim Chiang (SLAC) and Yoshitaka Hanabata  (Hiroshima) report on behalf of the Fermi LAT team:

At 04:35:45 (UT) on 03 Oct 2009, the Fermi Large Area Telescope (LAT) detected gamma rays from the long GRB 091003, which was triggered and located by the Fermi Gamma-ray Burst Monitor (GBM) (trigger 2756237347 / 091003191, GCN9983). The angle of the GBM best position (RA, Dec= 251.1, 37.2) with respect to the LAT boresight was ~13 degrees at the time of the trigger, which is close to the center of our field of view.

This burst was bright enough to initiate a Fermi spacecraft repointing maneuver resulting in 5 hours of pointed observations of the burst  position following the GBM trigger.

The data from the Fermi LAT shows a significant increase in the event rate after the GBM trigger that is spatially and temporally correlated with the GBM emission with high significance (>10 sigma).

The best LAT on-ground localization is found to be (RA, Dec = 251.39, 36.58) with a 90% containment radius of 0.21 deg (statistical; 68% containment radius: 0.15 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

Julie McEnery :

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.

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