GCN Circular 45721
GRB 260924A: Fermi-LAT detection of a bright burst
From: Rahul Gupta at NASA GSFC
Issued: 2026-09-24 12:00 UTC
Type: GRB, Gamma-ray Transient

A. Holzmann Airasca (UniTrento and INFN Bari), D. Depalo (Politecnico & INFN Bari), S. Cutini (INFN Perugia), Tamador Khalil (University of Johannesburg), and R. Gupta (NASA GSFC) report on behalf of the Fermi-LAT collaboration:


At 01:13:23 UT on September 24th, 2026, Fermi-LAT detected high-energy emission from GRB 260924A, which was also detected by Fermi-GBM (trigger 811905208/260924051, GCN #45712), Swift-BAT (GCN #45713), AstroSat CZTI (GCN #45720) and followed by Swift-XRT (GCN #45715), OSN telescope (GCN #45716), and NOT (GCN #45718).

The best LAT on-ground location is found to be

RA, Dec = 133.84, 12.01 (J2000)

with an error radius of 0.02 deg (90 % containment, statistical error only).

This was 62 deg from the LAT boresight at the time of the trigger.

The data from the Fermi-LAT show a significant increase in the event rate that is spatially and temporally correlated with the trigger with high significance.

The photon flux above 100 MeV in the time interval 0 - 1.1 ks after the GBM trigger is (8.3 ± 0.5)E-5 ph/cm2/s. The estimated photon index above 100 MeV is -2.2 ± 0.1. The highest-energy photon has an energy of 43.3 GeV and occurs at 77.5 s after the trigger time.

The Fermi-LAT point of contact for this burst is Sara Cutini (sara.cutini@pg.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.

Filter: gamma-ray bursts are posted only if in the top 10% of the past year's — by fluence (total energy received per cm², from Fermi GBM, Konus-Wind, GECAM and similar circulars; now ≥ 3.9×10^-5 erg/cm²) or by the number of GCN Circulars about the burst (now ≥ 14). Thresholds are recalculated monthly.
Relayed automatically from NASA's General Coordinates Network.