GCN Circular 45728
GRB 260922A: NuSTAR detection of prompt emission
From: Gaurav Waratkar at Caltech
Issued: 2026-09-24 15:41 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 260922A in both the NuSTAR CsI anti-coincidence shields. Details of the search algorithm will be described in a future paper.

The NuSTAR SINGS algorithm, triggered at 2026-09-22T10:00:33.95 UTC, shows a detection of GRB 260922A, also detected by Swift-BAT (GCN 45690) and CALET-GBM (GCN 45716).

The NuSTAR CsI shield data are recorded at 1 Hz. We detect a single peak lasting for about 10-s. The peak count rate is ~1500-cps with a baseline rate of ~1000-cps during this time period. We do not see any evidence in the signal above 100 keV in the CZT detectors.

The Swift-XRT localization (GCN 45696) at RA = 227.90847, Dec = 14.21907 implies an offset from the NuSTAR boresight of 44-deg (i.e. from the side) and an offset from the geocenter of 141-deg.

Lightcurves and analysis for this GRB can be found here:
Index of /NuSTAR_Public/grbs/reports/2026/260922A (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.
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