TITLE: GCN CIRCULAR NUMBER: 29368 SUBJECT: GRB 210126A: AstroSat CZTI detection DATE: 21/01/29 07:39:06 GMT FROM: Gaurav Waratkar at IIT,Bombay D. Nadella (NITK), G. Waratkar (IITB), A. Vibhute (IUCAA), S. Gupta (IUCAA), P. Sawant (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (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, 2020, arxiv:2011.07067) showed detection of a long GRB 210126A, which was also detected by Fermi-GBM (GCN #29354) and GECAM-B (GCN #29356). The source was detected in the 20-200 keV energy range in three quadrants (Quadrant A, C, and D). Quadrant D was noisy, and we excluded it from further analysis. The light curve showed multiple peaks of emission with the strongest peak at 2021-01-26 10:00:07 UT. The measured peak count rate associated with the burst is 56 (+9, -10) cts/s above the background in the combined data of two quadrants, with a total of 1039 (+412, -454) cts. The local mean background count rate was 248 (+1, -1) cts/s. Using cumulative rates, we measure a T90 of 67 (+41, -55) s. These large error bars arise from the presence of a weak second peak whose association with the burst is ambiguous in our data. CZTI GRB detections are reported regularly on the payload site at http://astrosat.iucaa.in/czti/?q=grb. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, ISAC, IUCAA, SAC and PRL. The Indian Space Research Organisation funded, managed and facilitated the project.