GCN Circular 10113
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 090926a (GCN 9933, Bissaldi et al.) over several epochs. For each epoch, total summed exposure times amounted to 36 minutes in I and 30 minutes in J. The afterglow of GRB 090926a (e.g. GCN 9937, Haislip et al.; GCN 9938, Gronwall et al.) is detected in our images with the following magnitudes (calibrated using Landolt standard stars in the optical and 2MASS stars in the IR): time post-burst I mag J mag 20.60 hrs 18.17+/-0.06 17.28+/-0.07 71.74 hrs 19.53+/-0.07 18.35+/-0.09 119.18 hrs 20.33+/-0.10 19.16+/-0.13 Between ~21 and 119 hours post-burst, the afterglow fades with a rate of alpha ~ -1.1+/-0.1 (where afterglow flux is proportional to t^alpha).