[vsnet-grb-info 13139] GRB 130427A: RAPTOR Bright Counterpart Before Swift Trigger

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  14476
SUBJECT: GRB 130427A: RAPTOR Bright Counterpart Before Swift Trigger
DATE:    13/04/28 00:12:42 GMT
FROM:    James Wren at LANL  <jwren at nis.lanl.gov>

J. Wren, W.T. Vestrand, P. Wozniak, and H. Davis,
of Los Alamos National Laboratory report:

Three RAPTOR full-sky persistent monitors at Maui, HI, and Los Alamos, NM,
independently detected  bright optical emission at the location of the
Swift trigger 554620 (Maselli, et al., GCN 14448).  Starting at 07:47:07.28
UT (50.2 seconds before the Swift trigger) we detect a brightening counterpart
which peaks at magnitude R~7.4.  After the peak, the source fades to below
10th magnitude at approximately the Swift trigger time.  The unfiltered images
from all three monitors are calibrated to the Tycho-2 V-band catalog.