TITLE: GCN CIRCULAR NUMBER: 19996 SUBJECT: GRB161004B: AstroSat CZTI detection DATE: 16/10/05 14:56:42 GMT FROM: Dipankar Bhattacharya at IUCAA V. Kumar, V. Sharma, D. Bhattacharya and V. Bhalerao (IUCAA), A. R. Rao (TIFR) and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration: Analysis of AstroSat CZTI data showed clear detection of GRB161004B (Swift BAT detection: D.Palmer et al., GCN Circ. 19987) in the 40-200 keV energy range. The light curve shows a single peak at 23:07:59.0 UT, coincident with the Swift Trigger. The measured peak count rate is 187.3 counts/sec above the background in combined data of four quadrants, with a total of 1393.0 counts. The local mean background count rate was 313.7 counts/sec. Using cumulative rates, we measure a T90 of 13.1 secs. 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.