GCN Circular 18228

GRB 150902A: Fermi-LAT detection

M. Arimoto (Tokyo Tech), M. Axelsson (KTH Stockholm), J. Racusin (NASA/GSFC), E. Bissaldi (INFN Bari),
D. Kocevski (NASA/GSFC) report on behalf of the Fermi-LAT team:

At 17:35:39.37 UT on 2015-09-02, Fermi-LAT detected high-energy emission from GRB 150902A,
which was also detected by Fermi-GBM (trigger 462908143/150902733).

The best LAT on-ground location is found to be

RA, Dec = 214.926, -69.361 degrees (J2000)

with an error radius of 0.127 deg (90% containment, systematic error only). This was 38 deg
from the LAT boresight at the time of the trigger and triggered an autonomous repoint of the
spacecraft.

The data from the Fermi-LAT show a significant increase in the event rate that is spatially and
temporally correlated with the GBM emission. More than 50 photons above 100 MeV and 9
photons above 1 GeV were observed within 300 seconds. The highest-energy photon is a 11 GeV
event which is observed ~100 seconds after the GBM trigger.

A Swift ToO has been requested for this burst.

The Fermi-LAT point of contact for this burst is Daniel Kocevski (daniel.kocevski@nasa.gov<mailto:daniel.kocevski@nasa.gov>).

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.