GCN Circular 5873
J. Wren, W.T. Vestrand, P.R. Wozniak, R. White, J. Pergande of Los Alamos National Laboratory report: Our autonomous Raptor-S telescope responded to Swift trigger 240766 (Sbarufatti et al. GCN 5854) at 08:48:17.29 UT, 20.87 s after the trigger and 4.3 s after receiving the GCN packet. Our first two images were obtained while the Swift BAT was still detecting emission from the GRB. We clearly detect a fading optical source at the location of the optical counterpart seen by the UVOT (Vanden Berk et al. GCN 5856). Our measurements show that the optical counterpart faded from magnitude R=12.3 to 14.4 over the first 90 seconds. Our unfiltered magnitudes were calibrated using the R-band magnitudes from the USNO B1.0 catalog.