{
  "submittedHow": "web",
  "body": "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:\n\nAnalysis of AstroSat CZTI data with the CIFT framework (Sharma et al., 2021, JApA, 42, 73) showed the detection of a long and bright GRB 250909B which was also detected by Konus-Wind (IPN notices).\n\nThe source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2025-09-09 17:49:11.50 UTC. The measured peak count rate associated with the burst is 701 (+50, -52) counts/s above the background in the combined data of all quadrants, with a total of 3971 (+218, -234) counts. The local mean background count rate was 282 (+4, -4) counts/s. Using cumulative rates, we measure a T90 of 10.1 (+0.9, -0.4) s.\n\nThe source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2025-09-09 17:49:10.32 UTC. The measured peak count rate associated with the burst is 1432 (+86, -93) counts/s above the background in the combined data of all quadrants, with a total of 5850 (+337, -369) counts. The local mean background count rate was 1344 (+7, -8) counts/s. We measure a T90 of 9.4 (+0.5, -0.3) s from the cumulative Veto light curve.\n\nCZTI 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.\n\nCZTI GRB detections are reported regularly on the payload site at:\nhttp://astrosat.iucaa.in/czti/?q=grb \n",
  "createdOn": 1757494711549,
  "format": "text/plain",
  "circularId": 41775,
  "subject": "GRB 250909B: AstroSat CZTI detection of a long burst",
  "submitter": "Anuraag Arya at IIT Bombay <aryaanuraag910@gmail.com>",
  "bibcode": "2025GCN.41775....1T",
  "eventId": "GRB 250909B"
}