GCN Circular 42664

S. Salunke (IUCAA), M. Tembhurnikar (IUCAA), Harsha K. H. (IUCAA), A. Goyal (IITB), A. Arya (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 251108C. This burst was also detected by the Konus-Wind team (priv. comm.) T0(KW) = 23:08:03.415 UT.

The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2025-11-08 23:07:57.38 UTC. The measured peak count rate associated with the burst is 250 (+36, -38) counts/s above the background in the combined data of all quadrants, with a total of 630 (+121, -124) counts. We caution that there is a 0.3 s readout dead time in CZT data during the burst which affects the calculated total counts. The local mean background count rate was 257 (+3, -4)   counts/s. Using cumulative rates, we measure a T90 of 7.0 (+1.8, -1.6) s. 

The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2025-11-08 23:07:56.96 UTC The measured peak count rate associated with the burst is 660 (+49, -53) counts/s above the background in the combined data of all quadrants, with a total of 3568 (+326, -374) counts. The local mean background count rate was 1128 (+7, -7) counts/s.  Using cumulative rates, we measure a T90 of 10.9 (+3.2, -3.0) s. 

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