GCN Circular 45750
GRB 260924A: Extreme Isotropic-equivalent Gamma-ray Energy and encouragement for multiwavelength follow-up observations
From: Rahul Gupta at NASA GSFC
Issued: 2026-09-25 19:48 UTC
Type: GRB

Rahul Gupta (NASA GSFC), Peter Veres (UAH), Vikas Chand (LSU), Eric Burns (LSU), Pádraig McDermott (University College Dublin), and L. Scotton (UAH) reports:

We have estimated the isotropic-equivalent gamma-ray energy of GRB 260924A (The Fermi GBM team, GCN 45712; D'Elia et al., GCN 45713; Salunke et al., GCN 45720; Holzmann Airasca et al., GCN 45721; McDermott et al., GCN 45723; Waratkar et al., GCN 45732; Gupta et al., GCN 45733; and Yu et al., GCN 45741) using the time-integrated Fermi-GBM spectrum and the measured redshift of z = 3.51 (Castro-Tirado et al. GCN 45740). 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 (McDermott et al., GCN 45723). Using the spectral parameters from McDermott et al., GCN 45723 and measured fluence of 2.84 × 10^-4 erg cm^-2 in the 10-1000 keV observer-frame energy range, and applying a bolometric k-correction to the 1-10,000 keV rest-frame energy range, we obtain an isotropic-equivalent gamma-ray energy of approximately 9.74 × 10^54 erg.

We adopted a flat Lambda-CDM cosmology with Omega_m = 0.286, Omega_Lambda = 0.714, and H0 = 69.6 km s^-1 Mpc^-1.

The inferred isotropic-equivalent energy places GRB 260924A among the most energetic gamma-ray bursts known. Its energetics are comparable, within the uncertainties, to those of GRB 221009A, the “BOAT” (Brightest Of All Time).

Given its extreme energetics and broad observational coverage, continued multi-wavelength observations of GRB 260924A are strongly encouraged.

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.
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