GCN Circular 38843
Subject
GRB 241228B: Fermi-LAT detection
Date
2025-01-07T18:46:55Z (2 days ago)
From
N. Di Lalla at Stanford University <niccolo.dilalla@stanford.edu>
Via
email
N. Di Lalla (Stanford University), A. Holzmann Airasca (UniTrento and INFN Bari), T. Khalil (Johannesburg Univ), S. Lopez (CNRS / IN2P3), D. Depalo (Politecnico and INFN Bari), C.C. Cheung (Naval Research Lab), C. Bartolini (UniTrento and INFN Bari) report on behalf of the Fermi-LAT Collaboration:
On December 28, 2024, Fermi-LAT detected high-energy emission from GRB 241228B, which was also detected by Fermi-GBM (trigger 757051990/241228176, GCN 38714), Swift-XRT (GCN 38713), Swift/BAT-GUANO (GCN 38700), GOTO24jmz (GCN 38684), TRT (GCN 38687), LCOGT (GCN 38692), GROWTH-India Telescope (GCN 38694), VLT/X-shooter (GCN 38704), LCO (GCN 38702), D50 (GCN 38715), SAO RAS (GCN 38733), 1.6m Mephisto (GCN 38739), 1.3m DFOT (GCN 38816).
The best LAT on-ground location is found to be:
RA, Dec = 127.8, 6.9 (J2000)
with an error radius of 0.1 deg (90 % containment, statistical error only).This was 56 deg from the LAT boresight at the time of the GBM trigger (T0 = 04:13:05.39 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 - 520 s after the GBM trigger is (1.2 +/- 0.3) E-5 ph/cm2/s. The estimated photon index above 100 MeV is 2.0 +/- 0.2. The highest-energy photon is a 16 GeV event which is observed about 31 seconds after the GBM trigger.
The Fermi-LAT point of contact for this burst is Francesco Longo (francesco.longo@ts.infn.it <mailto: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.