TITLE: GCN CIRCULAR NUMBER: 10111 SUBJECT: GRB 091029, SMARTS optical/IR afterglow observations DATE: 09/10/29 23:30:19 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 091029 (GCN 10097, Grupe et al.) with a mid-exposure time of 50 minutes post-burst (2009-10-29 04:43 UT). Total summed exposure times amounted to 36 minutes in I and 30 minutes in J. Imaging was done under poor (2.5") seeing conditions. The afterglow of GRB 091029 (e.g. GCN 10097, Grupe et al.; GCN 10098, Filgas et al.; GCN 10099, LaCluyze et al.) is detected in our images. Preliminary comparison to USNO-B1.0 stars in I and 2MASS stars in J indicates the following afterglow magnitudes: time post-burst I mag J mag 50 minutes 17.9+/-0.1 17.6+/-0.1 In individual I-band images, the afterglow fades by ~0.4 magnitudes between 30 and 69 minutes post-burst. During this time, the afterglow exhibits a shallow decay rate of alpha ~ -0.4+/-0.1 (where afterglow flux is proportional to t^alpha), which is consistent with the decay rate measured by LaCluyze et al. (GCN 10099).