GCN Circular 42752
Subject
GRB 251118A: Fermi-LAT detection
Event
Date
2025-11-19T05:39:12Z (2 days ago)
From
Rahul Gupta at NASA GSFC <rahul.gupta@nasa.gov>
Via
Web form
R. Gupta (NASA GSFC) and T. Khalil (Univ. of Johannesburg) report on behalf of the Fermi-LAT Collaboration:
On November 18 2025, Fermi-LAT detected high-energy emission from GRB 251118A, which was also detected by Fermi-GBM (trigger 785190695 / 251118855, GCN 42743). The best LAT on-ground location is found to be:
RA, Dec = 160.08, -34.58 (J2000)
with an error radius of 0.17 deg (90 % containment, statistical error only). This was 69 deg from the LAT boresight at the time of the GBM trigger (T0 = 20:31:30.09 UT).
The data from the Fermi-LAT shows 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 - 1.5 ks after the GBM trigger is (1.8 ± 0.7) E-6 ph/cm2/s. The estimated photon index above 100 MeV is -1.8 ± 0.3. The highest-energy photon is a 6.8 GeV event which is observed ~1400 seconds after the GBM trigger.
A Swift ToO has been approved for this burst.
The Fermi-LAT point of contact for this burst is Aldana Holzmann Airasca (a.holzmannairasca@unitn.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.