GCN Circular 45262

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 260730B 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 2026-07-30T13:13:45.0 UTC, shows a detection of GRB 260730B, also detected by SVOM-GRM (GCN notices). 

The NuSTAR CsI shield data are recorded at 1 Hz. We detect a single episode with two peaks lasting for about 25-s. The peak count rate is ~3500-cps with a baseline rate of ~1000-cps during this time period. We also see a signal above 100 keV in the CZT detectors.

Lightcurves and analysis for this GRB can be found here:
https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2026/260730B 

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.