TITLE: GCN CIRCULAR NUMBER: 9478 SUBJECT: GRB 090530: Early RAPTOR Optical Observations DATE: 09/06/02 00:37:08 GMT FROM: James Wren at LANL J. Wren, W.T. Vestrand, P.R. Wozniak, H. Davis, B. Norman of Los Alamos National Laboratory report: The RAPTOR telescope system responded to Swift trigger 353567 (Cannizzo et al., GCN 9438) under fair observing conditions. Our narrow-field instruments began observing the location at 03:18:37.96 UTC, 19.6 s after the Swift trigger. We detect the optical counterpart initially reported by Cannizzo et al. (GCN 9438) and Flewelling et al. (GCN 9439). Our first image at T+22.1 seconds shows the counterpart at R~17.1. It appears to brighten over the next minute reaching a peak near R~16.3 and then begins fading in the manner described by Schady et al. (GCN 9450) and Rossi et al. (GCN 9458). Our unfiltered images were calibrated against the USNO-B1 R-band. The following table gives selected observations, not corrected for extinction, from this event. t-mid(s) exp(s) mag mag-err -------------------------------------------- 22.08 5.0 17.13 0.25 57.90 5.0 16.30 0.10 84.50 5.0 16.60 0.13 133.21 10.0 16.87 0.11 414.65 30.0 17.31 0.09