TITLE: GCN CIRCULAR NUMBER: 39857 SUBJECT: GRB 250322B: NuSTAR detection of the prompt emission and regular dips during the burst DATE: 25/03/23 17:06:49 GMT FROM: Brian Grefenstette at Caltech/NuSTAR bwgref@srl.caltech.edu
B. Grefenstette (Caltech) reports 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 GRB 250322B in both the NuSTAR CsI anti-coincidence shields and in the CdZnTe detectors. 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 2025-03-22 20:08:06.000 with a resolution ~5-seconds. This is consistent with the detection by AstroSat CZT (Waratkar et al., GCN circ. 39848). The NuSTAR CsI shield data are recorded at 1 Hz.
The GRB appears to be a complex, broad burst with peak count rates near 4,000 cps over a baseline of ~1,000 cps. The burst lasts for over 100-s above background. We see clear evidence for correlated >100 keV X-rays in both CdZnTe focal planes for at least one of the multiple peaks in the burst.
Offline analysis of the CsI lightcurve shows complex features, including at least four quasi-periodic “dips” in the emission with intervals of roughly 20-s between the dips. A more detailed analysis of these features will follow.
Discovery report and a preliminary lightcurve for this GRB showing the dips can be found here:
https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2025/250322B/
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.
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