GCN Circular 15268
Subject
Fermi LAT Upper Limits on GRB 130925A
Event
Date
2013-09-28T00:03:12Z (12 years ago)
From
Daniel Kocevski at SLAC <dankocevski@gmail.com>
D. Kocevski, J. Racusin (NASA/GSFC), G. Vianello (Stanford), M. Axelsson
(Stockholm University), Nicola Omodei (Stanford) report on behalf of the
Fermi-LAT team:
A preliminary examination of the Fermi LAT data of the field containing GRB
130925A (Lien, et al., GCN 15246) has revealed no significant emission
above 40 MeV. The GRB was located ~22 degrees away from the LAT boresight
at the time of the first GBM detected emission associated with this burst
at 03:56:23.29 UT on 25 September 2013 (GCN 15255), hereafter T0(GBM), and
the subsequent autonomous repoint ensured that the source remained in the
field-of-view for the next ~2000s until it was occulted by the Earth.
Using an unbinned likelihood analysis, we estimate the following LAT upper
limits at 95% confidence for three separate time intervals, one covering
the entire 2000s that the source stayed in the LAT field-of-view, and two
of which correspond to the first and third emission episodes detected by
INTEGRAL/SPI-ACS (GCN 15259) and Konus-Wind (GCN 15260). We note that the
source was not in the LAT field-of-view during the second interval reported
in GCNs 15259 & 15260.
Interval 1: T0(GBM) to T0(GBM)+2000 = 7.3e-07 photons cm-2 s-1 (4.8e-10
ergs cm-2 s-1)
Interval 2: T0(GBM)+900s to T0(GBM)+1100s = 5.5e-06 photons cm-2 s-1
(3.6e-09 ergs cm-2 s-1)
Interval 3: T0(GBM)+4900 to T0(GBM)+5400 = 2.5e-06 photons cm-2 s-1
(1.6e-09 ergs cm-2 s-1)
This analysis covers an energy range of 0.1 to 10 GeV with a 12 deg
extraction region centered on the best known source position (GCN 15246