TITLE: GCN CIRCULAR NUMBER: 45728 SUBJECT: GRB 260922A: NuSTAR detection of prompt emission DATE: 26/09/24 15:41:00 GMT FROM: Gaurav Waratkar at Caltech 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: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2026/260922A Information on NuSTAR SINGS can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/ NuSTAR is a NASA Small Explorer mission led by Caltech and managed by JPL for NASA's Science Mission Directorate in Washington.