GCN 45267: GRB 260731A: AstroSat CZTI detection of a long burst

S.Salunke(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 GRB 260731A which was also detected by SVOM (Trigger Num. sb26073115) and Konus-Wind (IPN Notices).

The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve peaks at 2026-07-31 23:58:22.466 UTC. The measured peak count rate associated with the burst is 314 (+34, -33) counts/s above the background in the combined data of three quadrants (out of four), with a total of 2019 (+162, -264) counts. The local mean background count rate was 202 (+4, -3) counts/s. We measure a T90 of 11 (+3, -3) s from the cumulative CZT light curve. 

The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve peaks at 2026-07-31 23:58:21.203 UTC. The measured peak count rate associated with the burst is 417 (+49, -5) counts/s above the background in the combined data of all quadrants, with a total of 1801 (+233, -234) counts. The local mean background count rate was 591 (+3, -4) counts/s.
We measure a T90 of 8 (+4, -2) s from the cumulative Veto light curve.

CZTI data products like interactive and downloadable light curves for this GRB can be found at:https://astrosat.iucaa.in/cift/cift_products/ET20260731T235830/ET20260731T235830_details.html

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