TITLE:   GCN CIRCULAR
NUMBER:  6084
SUBJECT: GRB 070208: RAPTOR detection of early afterglow onset
DATE:    07/02/08 23:35:08 GMT
FROM:    James Wren at LANL  <jwren@nis.lanl.gov>

J. Wren, W.T. Vestrand, P.R. Wozniak, R. White, J. Pergande
of Los Alamos National Laboratory report:
 
Our Raptor-S telescope responded to Swift trigger 259714
(Sato et al., GCN 6074) at 09:11:17.10 UT, 42.8 s after the
trigger and 6.3 s after receiving the GCN packet.  We clearly
detect the source at the location of the optical counterpart
identified by Guidorzi et al. (GCN 6077).  Our first 5 second
exposure was obtained while the Swift BAT was still detecting
emission from the second GRB pulse (Markwardt et al., GCN 6081).
Our measurements show that the optical counterpart brightened
from fainter than magnitude 18.7 to 18.2 in the first 300
seconds after the trigger time and then began to fade steadily
after that.  Our unfiltered magnitudes were calibrated using
the R-band magnitudes from the USNO B1.0 catalog.