[vsnet-grb-info 13801] GRB 130821A: Fermi-LAT detection of a burst

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  15115
SUBJECT: GRB 130821A: Fermi-LAT detection of a burst 
DATE:    13/08/22 18:34:02 GMT
FROM:    Daniel Kocevski at SLAC  <dankocevski at gmail.com>

D. Kocevski (NASA/GSFC), N. Omodei (Stanford), J. Racusin (NASA/GSFC), S. Zhu (U. of Maryland), S. Guiriec (NASA/GSFC), Eleonora Troja (NASA/GSGC/UMCP) report on behalf of the Fermi-LAT team:

At 16:10:28.011 UT on 21 Aug 2013, Fermi-LAT detected high energy emission from GRB 130821A, which was also detected by Fermi-GBM (trigger 398794231/130821674 -- GCN 15113). The GBM detection triggered an autonomous repoint of the spacecraft.

The best LAT on-ground location is found to be RA=314.1, DEC=-12.0 (J2000) with an error radius of 0.1 deg (68% containment, statistical error only).

The burst was about 37 deg from the LAT boresight at the time of the trigger and the spacecraft slew brought the source within the LAT field of view for the next 2400 seconds. The data from the Fermi-LAT show long lasting emission with >40 photons above 100 MeV observed out to 2000s seconds with a TS of >170. Multi-peaked emission lasting roughly 40 seconds can be seen using the non-standard LAT Low Energy (LLE) with a significance of ~13 sigma. The highest energy LAT photon has an energy of ~6 GeV arriving 219 seconds after the trigger.

A Swift TOO request has been submitted.

The Fermi LAT point of contact for this burst is Daniel Kocevski (daniel.kocevski at 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.