[vsnet-grb-info 4417] GRB 070311: RAPTOR Detection of Optical Emission

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  6198
SUBJECT: GRB 070311: RAPTOR Detection of Optical Emission
DATE:    07/03/12 04:03:22 GMT
FROM:    James Wren at LANL  <jwren at nis.lanl.gov>

J. Wren, W.T. Vestrand, P.R. Wozniak, R. White, J. Pergande
of Los Alamos National Laboratory report:
 
Our Raptor telescopes responded to Integral trigger 6146
(Mereghetti et al., GCN 6189) at 01:53:16.10 UT, 26.1 s after
the trigger and 5.9 s after receiving the GCN packet.  We detected
optical emission from the IR counterpart reported by Covino et al.
(GCN 6190) and confirmed by Bloom et al. (GCN 6191).  Due to
twilight conditions we did not detect the optical counterpart while
the gamma-rays were still being detected by Integral (3-sigma
limiting magnitude R~15.5).  As the twilight period ended we detected
the counterpart at magnitude 17.8 +/- 0.2 in a 40 s image stack with
a mid-exposure time of 01:55:22.7 UT.  Subsequent image stacks show
fading of the counterpart.  Our unfiltered magnitudes were calibrated
using the R-band magnitudes from the USNO B1.0 catalog.