TITLE:   GCN CIRCULAR
NUMBER:  41979
SUBJECT: GRB 250924A: AstroSat CZTI detection
DATE:    25/09/25 06:29:43 GMT
FROM:    Gaurav Waratkar at Caltech <gauravwaratkar@iitb.ac.in>

M. Tembhurnikar (IUCAA), Harsha K. H. (IUCAA), S. Salunke (IUCAA), A. Arya (IITB), A. Goyal (IITB), G. Waratkar (Caltech/IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration:

Analysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a long-duration GRB 250924A which was also detected by Swift/BAT (Siegel et al., GCN Circ. 41959).

The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2025-09-24 08:18:32.00 UTC. The measured peak count rate associated with the burst is 48 (+17, -5) counts/s above the background in the combined data of three quadrants (out of four), with a total of 967 (+370, -133) counts. The local mean background count rate was 197 (+1, -3) counts/s. Using cumulative rates, we measure a T90 of 27 (+9, -5) s. 

The source was also faintly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range.

CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project.

CZTI GRB detections are reported regularly on the payload site at:
http://astrosat.iucaa.in/czti/?q=grb