TITLE: GCN CIRCULAR NUMBER: 44591 SUBJECT: GRB 260512A: NuSTAR detection of prompt emission DATE: 26/05/12 23:53:06 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 260512A 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 2026-05-12T16:56:43.530 UTC, shows a detection of GRB 260512A, also detected by Fermi/GBM (Fermi GBM Team, GCN 44542). The NuSTAR CsI shield data are recorded at 1 Hz. We detect a 10-s long burst consistent with the Fermi/GBM lightcurve. The peak count rate is ~2500-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 44542) at RA = 153.56, Dec = -82.64 implies an offset from the NuSTAR boresight of 15-deg (i.e. near the boresight) and an offset from the geocenter of 96-deg. Lightcurves and analysis for this GRB can be found here: https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2026/260512A 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/44591. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...