GCN Circular 45846
Subject
GRB 261007A / EP261007a: NuSTAR detection of prompt emission
Event
Date
2026-10-08T02:06:16Z (17 hours ago)
From
Gaurav Waratkar at Caltech <gauravwaratkar@iitb.ac.in>
Via
Web form
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 261007A, associated with EP261007a, in both the NuSTAR CsI anti-coincidence shields. This GRB was identified through a blind search using the CsI shield rates. Details of the search algorithm will be described in a future paper.
The NuSTAR SINGS algorithm triggered at 2026-10-07T05:39:49.7 UTC shows a detection of GRB 261007A, detected by SVOM (GCN 45824), Fermi-GBM (GCN 45830), and associated with EP261007a detected by Einstein Probe (GCN 45828).
The NuSTAR CsI shield data are recorded at 1 Hz. We detect a two-peak burst lasting for about 30-s, consistent with the GBM lightcurve. The peak count rate is ~4000-cps with a baseline rate of ~1000-cps during this time period. We also see a detection in the signal above 100 keV in the CZT detectors.
The optical counterpart (GCN 45825) at RA = 11.6142, Dec = -17.6922 implies an offset from the NuSTAR boresight of 87-deg and an offset from the geocenter of 78-deg.
Lightcurves and analysis for this GRB can be found here:
https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2026/261007A
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.