GCN Circular 37288
Subject
GRB 240825A: Fermi-LAT detection
Event
Date
2024-08-25T22:58:40Z (a year ago)
From
Rahul Gupta at NASA GSFC <rahulbhu.c157@gmail.com>
Via
email
N. Di Lalla (Stanford University), R. Gupta (NASA GSFC), and A. Holzmann
(DF, University of Buenos Aires, Argentina) report on behalf of the
Fermi-LAT Collaboration:
On Aug 25, 2024, Fermi-LAT detected high-energy emission from GRB 240825A,
which was also detected by Fermi-GBM (trigger 746293985 / 240825662, GCN
37273) and Swift-BAT (Gupta et al., GCN 37274).
The best LAT on-ground location is found to be:
RA, Dec = 344.56, 1.04 (J2000)
with an error radius of 0.07 deg (90 % containment, statistical error only).
This was 52 deg from the LAT boresight at the time of the GBM trigger: T0 =
15:53:00 UT.
The data from the Fermi-LAT show a significant increase in the event rate
that is spatially and temporally correlated with the GBM emission with high
significance. The photon flux above 100 MeV in the time interval 0-2000 s
after the GBM trigger is (2.9 +/- 0.2) E-5 ph/cm2/s. The estimated photon
index above 100 MeV is -2.65 +/- 0.09.
The highest-energy photon is a 40 GeV event which is observed ~ 240 seconds
after the GBM trigger.
The Fermi-LAT point of contact for this burst is Francesco Longo (
francesco.longo@ts.infn.it).
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.