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 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).