A. A. Miller, B. E. Cobb, J. S. Bloom, D. A. Perley (UC Berkeley), D.
Starr (UCB, LCOGT) report:
We observed the optical afterglow of GRB 081028 (Clemens et al., GCN
8424, Olofsson et al., GCN 8425) with the 1.3-m Peters Automated Infrared
Imaging Telescope (PAIRITEL). Observations with PAIRITEL began at 11:26:23
UT on Oct 28, 2008, 11 hours after the GRB trigger. We detect the
afterglow in a 3727 sec mosaic of 7.8 sec simultaneous exposures in the
J, H, and Ks filters. Preliminary photometry for the afterglow in these
mosaics with midtime 12:13:59 Oct 28, 2008 UT yields J = 17.7 +- 0.1, H =
17.0 +- 0.1, and Ks = 16.1 +- 0.1 (all magnitudes given in the Vega
system), calibrated to the 2MASS system. In intermediate mosiacs we find
that the afterglow gets brighter during our ~1.5 hrs of observations. No
correction for Galactic extinction (E(B-V) = 0.03; Schlegel et al. 1998)
has been made to the above reported values.
These measurements indicate that the burst afterglow became
brighter and redder following the measurements made by Clemens et al.
(GCN 8424). Schady & Guidorzy (GCN 8431) report an optical brightening of
the afterglow, consistent with the detected behavior in the NIR, around
the time of our observations, and further measurements by Clemens et al.
(GCN 8442) taken roughly 31 hours after the burst trigger show that the
afterglow is redder than their initial observations.