TITLE: GCN CIRCULAR NUMBER: 13818 SUBJECT: GRB 120923A: RAPTOR Early Afterglow Limits DATE: 12/09/25 23:45:36 GMT FROM: James Wren at LANL J. Wren, W.T. Vestrand, P. Wozniak, and H. Davis, of Los Alamos National Laboratory report: The RAPTOR network of robotic optical telescopes made follow-up observations of Swift trigger 534402 (Yershov, et al., GCN 13796). Our narrow-field instruments in Los Alamos, NM, began imaging at 05:17:43.06 UT, 96.8 s after the Swift BAT trigger. We do not detect the optical counterpart (Levan, et al., GCN 13802) in any of our images. The following table summarizes some of our early observations. Our unfiltered images are calibrated to the USNO-B1 r-band. The start time is seconds since the BAT trigger time. The magnitude limit is the 3-sigma detection threshold. T-Start Exp-Time Mag-Limit ---------------------------------- 96.82 5.9 17.3 106.83 5.4 17.6 143.24 5.4 17.5 161.53 5.1 17.5 181.82 10.1 18.2 220.22 10.4 18.1 284.22 10.9 18.1