GCN Circular 15399

J. L. Racusin (NASA/GSFC), G. Vianello (Stanford), Elisabetta Bissaldi (University & INFN Trieste), Rachele Desiante 
(University of Udine and INFN Trieste), Francesco Longo (University and INFN Trieste), report on behalf of 
the Fermi-LAT team:

Starting around 23:20:48.58 on October 29, 2013 Fermi LAT detected high energy emission from GRB 131029A, 
which was also detected by Fermi-GBM (trigger 404781651/131029973).

The best LAT on-ground location is found to be RA, DEC 200.785, 48.298 (J2000) with an error radius of 0.26 deg 
(68% containment, statistical error only), this was 60 deg from the LAT boresight at the time of the trigger (i.e., close 
to the limit of the LAT field of view). This position is ~6 deg away from the best available GBM position, well within 
the error radius if we include a typical systematic error of 3 deg.  The burst position was observed by the LAT from 
the trigger until ~T0+800 s.

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 with high significance. More than 
19 photons above 100 MeV and more than 3 photons above 1 GeV are observed within 800 seconds. The highest 
energy photon is a 1.3 GeV event which is observed 70 seconds after the GBM trigger.

A Swift ToO has been requested for this burst.

The Fermi LAT point of contact for this burst is Judith Racusin (judith.racusin@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.