GCN Circular 7464
P. Wozniak, W.T. Vestrand, J. Wren, and H. Davis (Los Alamos National Laboratory) The RAPTOR sky monitoring system began observing the location of GRB 080319B more than an hour before the Swift BAT trigger 306757 (Racusin et al., GCN 7427). The first exposure with detectable optical emission started ~2 seconds after the trigger at 06:12:50.9 UT. A peak brightness of 5.6 mag was recorded in time interval from 06:13:21.2 to 06:13:31.2 UT, before the end of the gamma-ray emission. Using the redshift z=0.937 from Vreeswijk et al. (GCN 7444) the estimated luminosity of GRB 080319B exceeds that of GRB 990123. Our response arrays RAPTOR-P and T began imaging at 06:14:24.3 UT following the XRT localization trigger that interrupted the ongoing follow-up measurements of GRB 080319A. The OT is detected by both response instruments including all channels (V,R,I,clear) of the simultaneous multicolor imager RAPTOR-T.