TITLE:   GCN CIRCULAR
NUMBER:  8339
SUBJECT: GRB 081007, SMARTS optical afterglow observations
DATE:    08/10/08 01:49:15 GMT
FROM:    Bethany Cobb at Yale U  <bcobb@astro.berkeley.edu>

B. E. Cobb (UC Berkeley) reports:

Using the ANDICAM instrument on the 1.3m telescope at CTIO, we
continued to obtain optical/IR imaging of the error region of GRB 081007
(GCN 8330, Baumgartner et al.) following GCN 8332.

At a mid-exposure time of 2008-10-07 06:04 UT (40 minutes post-burst),
the GRB afterglow (GCN 8330, Baumgartner et al.) had the following
magnitudes:
B = 19.36 +/- 0.04
R = 18.37 +/- 0.03
I = 17.73 +/- 0.03

Observations were obtained under non-photometric conditions.  These
preliminary magnitudes are calibrated against several USNO-B1.0 stars in
the field, so there is likely an additional photometric calibration error
of ~0.2 magnitudes.

From 23 minutes to 112 minutes post-burst the decay rate of the
afterglow remains at alpha = -0.6 (where afterglow flux is proportional to
t^alpha) in all our optical colors.

Further observations of this burst are planned.