GCN Circular 45732
GRB 260924A: NuSTAR detection of prompt emission
From: Gaurav Waratkar at Caltech
Issued: 2026-09-24 19:26 UTC
Type: GRB, X-ray Transient

G. Waratkar (Caltech) and B. Grefenstette (Caltech) report on behalf of the NuSTAR Search for INteresting Gamma-ray Signals (SINGS) working group:

The NuSTAR SINGS working group reports the detection of prompt emission from the long-duration GRB 260924A in both the NuSTAR CsI anti-coincidence shields. This GRB was identified through a blind search using the CsI shield rates. Details of the search algorithm will be described in a future paper.

The NuSTAR SINGS algorithm triggered at 2026-09-24T01:13:23.56 UTC shows a detection of GRB 260924A, also detected by Fermi-GBM (GCN 45712), Swift-BAT (GCN 45713), and AstroSat-CZTI (GCN 45720).

The NuSTAR CsI shield data are recorded at 1 Hz. We detect a multi-peaked burst lasting for about 150-s, consistent with the GBM, BAT and CZTI lightcurves. The peak count rate is ~1500-cps with a baseline rate of ~1000-cps during this time period. We also see a detection in the signal above 100 keV in the CZT detectors.

The Swift-XRT localization (GCN 45713) at RA = 133.7620, Dec = 12.0455 implies an offset from the NuSTAR boresight of 130-deg and an offset from the geocenter of 158-deg.

Lightcurves and analysis for this GRB can be found here:
Index of /NuSTAR_Public/grbs/reports/2026/260924A (nustarsoc.caltech.edu)

Information on NuSTAR SINGS can be found here:
NuSTAR Search for INteresting Gamma-ray Signals (SINGS) (nustarsoc.caltech.edu)

NuSTAR is a NASA Small Explorer mission led by Caltech and managed by JPL for NASA's Science Mission Directorate in Washington.

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.