[vsnet-grb-info 6737] GRB 081007: Early RAPTOR measurements of optical counterpart

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  8337
SUBJECT: GRB 081007: Early RAPTOR measurements of optical counterpart
DATE:    08/10/07 19:56:45 GMT
FROM:    James Wren at LANL  <jwren at nis.lanl.gov>

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

The RAPTOR telescope system responded to Swift trigger
330856 (Baumgartner et al., GCN 8330) under fair observing conditions.
Our narrow-field instruments began observing the location at
05:24:17.13 UTC, 24.4 s after the Swift trigger and during the end
of the Gamma-Ray emitting interval.  We detect the optical counterpart
reported by Baumgartner et al. (GCN 8330) and Covino et al. (GCN 8331).
We first detect the counterpart at R~16.4 at approximately 90s after
the Swift trigger time.  The counterpart brightens over the next 50
seconds to magnitude R~15.4 and then begins fading steadily.  Our
unfiltered images were calibrated against the USNO-B1 R-band.  The
following table gives selected observations, not corrected for
extinction, from this event.

t-mid(s)    exp(s)     mag     mag-err
--------------------------------------------
90.31        5.0      16.43    0.22
139.58      10.0      15.38    0.06
367.83      30.0      16.75    0.20
685.42      30.0      17.28    0.19