GCN Circular 12784
Using the ANDICAM instrument on the 1.3m telescope at CTIO, we obtained optical/IR imaging of the error region of GRB 111228A (GCN 12737, Ukwatta et al.) with a mid-exposure time of 15.9 hours (2011-12-29 07:39 UT) and 39.5 hours (2011-12-30 07:13 UT) post-burst. Total summed exposure times amounted to 36 minutes in I and 30 minutes in J. The optical afterglow of GRB 111228A (e.g. GCN 12737, Ukwatta et al.; GCN 12738, Xin et al.) is detected and observed to decay between our imaging. Preliminary comparison to Landolt standard stars in the optical and 2MASS stars in the IR indicates the following magnitudes for the afterglow: time post-burst I mag J mag 15.9 hours 19.3 +/- 0.1 20.6 +/- 0.1 39.5 hours 18.4 +/- 0.1 > 19.1 (3-sigma limit) This indicates that the decay rate of the burst between ~16 and 40 hours post burst is alpha ~ 1.3 (where afterglow flux is proportional to t^-alpha). In agreement with Cenko et al. (GCN 12771), this later-time decay is much steeper than the earlier-time decay noted by Klotz et al. (GCN 12742) and Pandey et al. (GCN 12745).