TITLE: GCN CIRCULAR NUMBER: 21093 SUBJECT: GRB 170510A: AstroSat CZTI(Veto) detection DATE: 17/05/14 18:59:22 GMT FROM: Vidushi Sharma at IUCAA V. Sharma (IUCAA), V. Bhalerao (IIT-B), D. Bhattacharya (IUCAA), A. R. Rao (TIFR), S. Vadawale (PRL) report on behalf of the Astrosat CZTI collaboration: The bright long GRB170510A (Bissaldi E. et al., GCN Circ. 21080) was detected using the CsI veto detectors on Astrosat CZTI (Bhalerao et al., arXiv:1608.03408). The source was clearly detected in the 125-250 keV energy range. The light curve shows a multiple peak structure. The peak count rate in the CsI detectors was 940.2 counts/sec above the background (four quadrants summed together), with a total of 699536 counts. The local mean background count rate was 1365.7 counts/sec. Using cumulative rates, we measure a T90 of 67.8 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.