TITLE: GCN CIRCULAR NUMBER: 42324 SUBJECT: GRB 251016B: AstroSat CZTI detection DATE: 25/10/17 10:34:55 GMT FROM: Anuraag Arya at IIT Bombay aryaanuraag910@gmail.com
Harsha K. H. (IUCAA), M. Tembhurnikar (IUCAA), S. Salunke (IUCAA), A. Arya (IITB), U. Pathak (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 bright,long GRB 251016B which was also detected by Fermi GBM (Fermi GBM Team, GCN Circ. 42316).
The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2025-10-16 23:59:03.85 UTC. The measured peak count rate associated with the burst is 1394 (+217, -85) counts/s above the background in the combined data of three quadrants (out of four), with a total of 4295 (+210, -209) counts. The local mean background count rate was 214 (+6, -8) counts/s. Using cumulative rates, we measure a T90 of 5.4 (+0.8, -0.5) s. In the preliminary analysis, we find 498 Compton events associated with this event.
The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2025-10-16 23:59:02.60 UTC. The measured peak count rate associated with the burst is 1972 (+90, -100) counts/s above the background in the combined data of all quadrants, with a total of 6747 (+290, -334) counts. The local mean background count rate was 1255 (+6, -6) counts/s. We measure a T90 of 5.2 (+1.8, -0.7) 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
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