GCN Circular 45723
GRB 260924A: Fermi GRB Observation
From: Padraig McDermott at University College Dublin
Issued: 2026-09-24 13:56 UTC
Type: GRB, Gamma-ray Transient

Pádraig McDermott (University College Dublin), and L. Scotton (UAH) report on behalf of the Fermi Gamma-ray Burst Monitor Team:

"At 01:13:23.56 UT on 24 September 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260924A (trigger 811905208/260924051), which was also detected by Swift-BAT (D'Elia et al. 2026, GCN 45713), Swift-XRT (Evans et al. 2026, GCN 45715), AstroSat CZTI (Salunke et al. 2026, GCN 45720), and Fermi-LAT (Holzmann Airasca et al. 2026, GCN 45721)

An optical counterpart is identified by the 1.5m OSN (Hu et al. 2026, GCN 45717), and NOT (Izzo et al. 2026, GCN 45718).

The Fermi GBM real-time localization (GCN 45712) is consistent with the Swift BAT position.

The angle from the Fermi LAT boresight is 62 degrees.

The GBM light curve consists of three seperate emission episodes with a duration (T90) of about 337.9 s (50-300 keV). The time-averaged spectrum from T0-11.6 to T0+382.6 s is best fit by a Band function with Epeak = 645 +/- 4 keV, alpha = -0.91 +/- 0.01, and beta = -2.36 +/- 0.01.

The event fluence (10-1000 keV) in this time interval is (2.84 +/- 0.01)E-04 erg/cm^2. The 1-sec peak photon flux measured starting from T0+343.5 s in the 10-1000 keV band is 19.2 +/- 0.3 ph/s/cm^2.

The spectral analysis results presented above are preliminary; final results will be published in the GBM GRB Catalog: FERMIGBRST - Fermi GBM Burst Catalog (heasarc.gsfc.nasa.gov)

For Fermi GBM data and info, please visit the official Fermi GBM Support Page: https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/";

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.