TITLE:   GCN CIRCULAR
NUMBER:  35564
SUBJECT: GRB 240118A: NuSTAR Detection of a Long GRB
DATE:    24/01/18 17:14:54 GMT
FROM:    Brian Grefenstette at Caltech/NuSTAR <bwgref@srl.caltech.edu>

B. Grefenstette 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 of the GRB 240118A in the NuSTAR CsI anti-coincidence shields. Thus GRB was identified through a blind search using the CsI shield rates with a trigger time (2024-01-18 01:48:46). This is consistent with the time of the delayed large peak seen in the GBM lightcurve from Fermi GBM (Fermi Team GCN 35558, Hamburg GCN 35563) which arrives ~40-sec after the initial GBM trigger at 01:48:09. Data from the CdZnTe detectors have not yet been downloaded from the spacecraft.

The burst shows at least three broad peaks in the CsI shields from both NuSTAR FPMs, peaking at 3000-5000 counts per second (the background in the shields was roughly 1000 cps).

The automated light curve report for this GRB and discovery report can be found here:

https://nustarsoc.caltech.edu/NuSTAR_Public/grbs/reports/2024/240118A/

…where further offline analysis will be performed once more data are downloaded from NuSTAR.