TITLE: GCN CIRCULAR NUMBER: 7570 SUBJECT: GRB 080319A: Early RAPTOR optical limits DATE: 08/04/08 20:42:18 GMT FROM: James Wren at LANL J. Wren, W.T. Vestrand, P.R. Wozniak, H. Davis of Los Alamos National Laboratory report: Our RAPTOR telescopes imaged the location of Swift trigger 306754 (Pagani et al., GCN 7426). We do not detect the optical counterpart initially reported by Cenko et al. (GCN 7429). The location of the counterpart was within the field of view of our continuous all-sky monitoring system. We can place 5 sigma limits at approximately magnitude 9.0 during the time period within 5 minutes both before and after the trigger. Our narrow-field instruments began observing the location at 05:46:51.90 UTC, 69.8 s after the Swift trigger, but also did not detect the counterpart. The limiting magnitudes of our unfiltered observations when calibrated to the USNO-B1 R-band are given in the following table. t-mid(s) exp(s) mag mag-err -------------------------------------------- -19.18 10.0 9.0 5 sigma limit 14.07 10.0 9.0 5 sigma limit 72.35 5.0 16.9 5 sigma limit 156.60 10.0 17.4 5 sigma limit 423.25 30.0 18.0 5 sigma limit