TITLE:   GCN CIRCULAR
NUMBER:  41771
SUBJECT: GRB 250909A: AstroSat CZTI detection
DATE:    25/09/10 06:35:24 GMT
FROM:    Anuraag Arya at IIT Bombay <aryaanuraag910@gmail.com>

A. Goyal (IITB), A. Arya (IITB), M. Tembhurnikar (IUCAA), Harsha K. H. (IUCAA), S. Salunke (IUCAA), G. Waratkar (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 250909A which was also detected by Fermi GBM (Fermi GBM Team, GCN Circ. 41753).

The source was detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed a burst peak of emission at 2025-09-09 02:33:32.44 UTC. The measured peak count rate associated with the burst is 228 (+61, -66) counts/s above the background in the combined data of all quadrants, with a total of 663 (+255, -303) counts. The local mean background count rate was 1258 (+7, -5) counts/s. We measure a T90 of 8.2 (+2.5, -4.0) s from the cumulative Veto light curve.

The source was also faintly detected in the CZT detectors in the 20-200 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