GCN Circular 41628

Harsha K H (IUCAA), A. Arya (IITB), M. Tembhurnikar (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 bright GRB 250830C which was also detected by Konus-Wind (IPN notices). We note that this burst is towards the tail end of solar activity as seen in GOES data.

The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2025-08-30 14:52:21.50 UTC. The measured peak count rate associated with the burst is 248 (+42, -14) counts/s above the background in the combined data of two quadrants (out of four), with a total of 1394 (+282, -55) counts. The local mean background count rate was 135 (+5, -9) counts/s. Using cumulative rates, we measure a T90 of 9.5 (+4.8, -0.7) 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 2025-08-30 14:52:21.29 UTC. The measured peak count rate associated with the burst is 1516 (+85, -91) counts/s above the background in the combined data of all quadrants, with a total of 7100 (+323, -375) counts. The local mean background count rate was 1307 (+5, -4) counts/s. We measure a T90 of 9.2 (+1.5, -0.9) s from the cumulative Veto light curve.

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