TITLE: GCN CIRCULAR NUMBER: 7403 SUBJECT: GRB 080310: early RAPTOR multicolor observations DATE: 08/03/10 22:05:02 GMT FROM: Przemyslaw R. Wozniak at LANL P. Wozniak, W.T. Vestrand, J. Wren, and H. Davis (Los Alamos National Laboratory) Our RAPTOR-S and RAPTOR-T telescopes began simultaneous multicolor (clear, V, R, I) imaging of GRB 080310 at UT 08:38:27.14, 28.5 seconds after the trigger, 6.7 seconds after receiving the trigger. The counterpart identified by Chornok et al. (GCN 7381) brightened from below 17 mag to about 16.8 mag at ~200 seconds (clear band calibrated to USNO B1.0 R2 magnitudes) and dimmed to about 17.3 mag at 400 seconds. We clearly detect the OT simultaneously in all filters and follow its flux evolution for 1.5 hours. We observe a broad plateau between 400 and 1100 seconds with slight rebrightening towards the end of this time interval, folowed by rapid decay.