TITLE: GCN CIRCULAR NUMBER: 23250 SUBJECT: GRB 180914B: AstroSat CZTI detection DATE: 18/09/17 20:55:04 GMT FROM: Vidushi Sharma at IUCAA T. Khanam, V. Sharma 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 180914B, which was also detected by AGILE (MCAL: Ursi A. et al., GCN 23226 and GRID: Verrecchia F. et al., GCN 23231), Fermi-LAT (Bissaldi E. et al., GCN 23232), Swift-XRT (D'Ai A. et al., GCN 23236) and Konus-Wind (Frederiks D. et al., GCN 23240). The source was clearly detected in the 40-200 keV energy range. The light curve shows multiple peaks of emission with strongest peak at 18:23:02.500 UT. The measured peak count rate is 3258 cts/s above the background in combined data of four quadrants, with a total of 105168 cts. The local mean background count rate was 657 cts/s. Using cumulative rates, we measure a T90 of 146.8 s. In preliminary analysis, we find that 7300 compton events are associated with this event. 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.