TITLE:   GCN CIRCULAR
NUMBER:  14013
SUBJECT: GRB 121128A: RAPTOR Detection During Gamma-Ray Emitting Interval
DATE:    12/11/28 16:42:41 GMT
FROM:    James Wren at LANL  <jwren@nis.lanl.gov>

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 539866 (Oates, et al., GCN 14007).  Our narrow-field
RAPTOR-S telescope located in Los Alamos, NM, began imaging at 05:06:12.6 UT,
35.4 s after the Swift BAT trigger and during the period that the BAT was
still detecting gamma-ray emission (Palmer, et al., GCN 14011).  Starting
during the gamma-ray emitting interval we detect a brightening counterpart
that ultimately peaks at T+75s with a R-band equivalent magnitude of
approximately 13.9 before beginning to fade.  Our unfiltered images are
calibrated to the USNO-B1 R-band.