[vsnet-grb-info 6860] GRB 081029, SMARTS optical/IR afterglow observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  8452
SUBJECT: GRB 081029, SMARTS optical/IR afterglow observations
DATE:    08/10/29 23:19:48 GMT
FROM:    Bethany Cobb at UC Berkeley  <bcobb at astro.berkeley.edu>

B. E. Cobb (UC Berkeley) reports:

Using the ANDICAM instrument on the 1.3m telescope at CTIO, we obtained 
optical/IR imaging of the error region of GRB 081029 (GCN 8435, Sakamoto 
et al.) at three epochs with mid-exposure times of 2008-10-29 04:18 UT 
(2.57 hrs post-burst), 04:50 UT (3.10 hrs post-burst) and 05:21 UT (3.62 
post-burst).  At each epoch, several dithered images were obtained in each 
filter, with total summed exposure times of 180s in each of BRIJK and 120s 
in each of H and V.

The GRB afterglow (e.g. GCN 8436, Rykoff et al. and GCN 8437, Clemens et 
al.) is detected in all our filters:

filter  2.57 hrs	3.10 hrs	3.62 hrs
B       19.69+/-0.04 	19.85+/-0.04   	20.00+/-0.05
V       18.26+/-0.03  	18.38+/-0.03   	18.57+/-0.04
R       17.32+/-0.02  	17.50+/-0.02   	17.66+/-0.02
I       16.79+/-0.03   	16.94+/-0.03   	17.15+/-0.03
J       15.83+/-0.08   	16.02+/-0.08   	16.03+/-0.08
H       15.00+/-0.08   	15.13+/-0.08   	15.32+/-0.08
K       14.25+/-0.08  	14.35+/-0.08   	14.60+/-0.08

These preliminary magnitudes are calibrated using Landolt standard stars 
in the optical and 2MASS stars in the IR.

Between 2.57 hrs and 3.62 hours post-burst, the afterglow decays with an 
approximate optical decay rate of alpha~-0.9 (where afterglow flux
is proportional to t^alpha).