TITLE: GCN CIRCULAR NUMBER: 44302 SUBJECT: GRB 260415B: NuSTAR detection of long prompt emission DATE: 26/04/15 22:13:57 GMT FROM: Gaurav Waratkar at Caltech <gauravwaratkar@iitb.ac.in> 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 260415B 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 2026-04-15T02:28:55.54 UTC, shows a detection of GRB 260415B, also detected by Fermi/GBM (Fermi GBM Team, GCN 44300) and CALET/GBM (Trigger 1460255329). The NuSTAR CsI shield data are recorded at 1 Hz. We detect a ~30-s burst followed by a ~20-s burst after a ~20-s gap, consistent with CALET/GBM and the broad bright Fermi/GBM peak at ~200 s post-trigger. The peak count rate is ~1500-cps with a baseline rate of ~1000-cps during this time period. We do not see evidence in the signal above 100 keV in the CZT detectors. The Fermi/GBM localization (GCN 44300) at RA = 229.43, Dec = 24.94 implies an offset from the NuSTAR boresight of 71-deg (i.e. from the side of the instrument) and an offset from the geocenter of 107-deg. Lightcurves and analysis for this GRB can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2026/260415B 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. View this GCN Circular online at https://gcn.nasa.gov/circulars/44302. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...