TITLE: GCN CIRCULAR NUMBER: 29367 SUBJECT: GRB 210124B: AstroSat CZTI detection DATE: 21/01/29 06:12:31 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 the short GRB 210124B, which was also detected by Insight-HXMT/HE (GCN #29353) & Konus-Wind (GCN #29357). The source was clearly detected in the 20-200 keV energy range in all four quadrants. Quadrant D was noisy, and we excluded it from further analysis. The light curve showed multiple peaks of emission with the strongest peak at 2021-01-24 13:23:45.43 UT. The measured peak count rate associated with the burst is 2348 (+928, -540) cts/s above the background in the combined data of three quadrants, with a total of 88 (+52, -26) cts. The local mean background count rate was 362 (+2, -25) cts/s. Using cumulative rates, we measure a T90 of 0.07 (+0.35, -0.04) s. 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.