TITLE: GCN CIRCULAR NUMBER: 33415 SUBJECT: GRB 230307A: AstroSat CZTI detection DATE: 23/03/08 06:17:52 GMT FROM: Gaurav Waratkar at IIT,Bombay P K. Navaneeth (IUCAA), G. Waratkar (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 the extremely bright long GRB 230307A which was also detected by Fermi-GBM (Fermi GBM team, GCN 33405), GECAM (Xiong et al., GCN 33406), Solar Orbiter STIX (Xiao et al., GCN 33410), AGILE/MCAL (Casentini et al., GCN 33412) and IPN (Kozyrev et al., GCN 33413). The source was clearly detected in the 20-200 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2023-03-07 15:44:10.0 UTC. The measured peak count rate associated with the burst is 4041 (+33, -37) counts/s above the background in the combined data of all quadrants, with a total of 90900 (+758, -850) counts. The local mean background count rate was 453 (+1, -1) counts/s. Using cumulative rates, we measure a T90 of 33 (+1, -1) s. In the preliminary analysis, we find 5484 Compton events associated with this event. It was also clearly 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 2023-03-07 15:44:15.17 UTC. The measured peak count rate is 276156 (+268, -300) counts/s above the background in the combined Veto data of all quadrants, with a total of 5571313 (+4953, -6044) counts. The local mean background count rate was 14750 (+7, -6) counts/s. We measure a T90 of 40 (+0.2, -0.2) 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