J. Wren, W.T. Vestrand, P.R. Wozniak, R. White, J. Pergande of Los Alamos National Laboratory report: ivo:/raptor.lanl# RAPTOR Los Alamos National Laboratory Robert White +1-505-665-3025 rwhite@lanl.gov 2007-04-19T17:11:29 2007-04-19T10:00:50 182.7451 39.9261 0.0166666666666667 optical transient GRB 070419a Our Raptor telescopes responded to Swift trigger 276205 (Stamatikos et al., GCN 6302) at 10:00:49.8 UT, 83.7 s after the trigger and 7.8 s after receiving the GCN packet. We detect optical emission from the counterpart reported by the KAIT team (Chornock et al., GCN 6304). Our observations show that the counterpart brightened from below magnitude 18.8 to 18.44 (+- .15) at a mid-exposure time of 10:09:27.9 UT (60s duration). The counterpart then began a slow decline but remained detectable in our images until we interrupted our observing sequence at 10:47:17 UT for Swift trigger 276212. Our unfiltered images were calibrated using the R-band magnitudes from the USNO B1.0 catalog.