TITLE: GCN CIRCULAR NUMBER: 22762 SUBJECT: GRB 180603A: AstroSat CZTI detection DATE: 18/06/05 08:56:37 GMT FROM: Vidushi Sharma at IUCAA V. Sharma, A. Vibhute and D. Bhattacharya (IUCAA), V. Bhalerao (IIT-B), A. R. Rao (TIFR) and S. Vadawale (PRL) report on behalf of the Astrosat CZTI collaboration: Analysis of Astrosat CZTI data showed the detection of a long GRB 180603A at 16:23:00.0 UT. The source was clearly detected in the 40-200 keV energy range. The light curve shows multiple peaks of emission with strongest peak at 16:23:15.5 UT. The measured peak count rate is 609.2 cts/s above the background in combined data of four quadrants, with a total of 7198 cts. The local mean background count rate was 505.8 cts/s. Using cumulative rates, we measure a T90 of 31.1 s. It was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. 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.