TITLE: GCN CIRCULAR NUMBER: 46089 SUBJECT: GRB 261029A : AstroSat CZTI detection DATE: 26/10/29 13:26:02 GMT FROM: ABHINAV GOYAL at Indian Institute of Technology Bombay S. Salunke (IUCAA), Harsha K. H. (IUCAA), A. Goyal (IITB), A. Arya (IITB), S. Puri (IITB), G. Waratkar (Caltech/IITB), V. Bhalerao (IITB), A. Vibhute (IUCAA), 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 GRB 261029A which was also detected by Fermi (Fermi GBM team, GCN Circ. 46071), SVOM (Goto et. al., GCN Circ. 46072) and Fermi LAT (Gupta et. al., GCN Circ. 46085). The source was 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 2026-10-29 01:27:42.65 UTC. The measured peak count rate associated with the burst is 775 (+53, -54) counts/s above the background in the combined data of all four quadrants, with a total of 8463 (+365, -387) counts. The local mean background count rate was 275 (+2, -3) counts/s. We measure a T90 of 38 (+1, -1) s from the cumulative CZT light curve. The source was also 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 2026-10-29 01:27:42.98 UTC. The measured peak count rate associated with the burst 2526 (+89, -89) counts/s above the background in the combined data of all four quadrants, with a total of 27187 (+557, -595) counts. The local mean background count rate was 624 (+4, -4) counts/s. We measure a T90 of 37 (+1, -1) s from the cumulative Veto light curve. In the preliminary analysis, we find 1151 Compton events associated with this event. CZTI data products like interactive and downloadable light curves for this GRB can be found at: https://astrosat.iucaa.in/cift/cift_products/ET20261029T012733/ET20261029T012733_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