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GCN Circular 9867

GRB 090902B: Fermi LAT detection
2009-09-02T22:48:18Z (15 years ago)
Hiroyasu Tajima at SLAC <>
Francesco de Palma (Universit� 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 (

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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