GCN Circular 6347
B. E. Cobb (Yale), part of the larger SMARTS consortium, reports: Using the ANDICAM instrument on the 1.3m telescope at CTIO, we obtained optical/IR imaging of the error region of GRB 070420 (GCN 6330, Stamatikos et al.) with a mid-exposure time of 2007-04-21 01:15 UT (~18.9 hrs post-burst) and again at 2007-04-23 00:52 UT (~66.6 hrs post-burst). For each set of observations, total summed exposure times amounted to 36 minutes in I and 30 minutes in J. The afterglow of GRB 070420 (GRB 6330, Stamatikos et al.) is detected in the first epoch images and is observed to fade between the first and second epochs by approximately 1 magnitude. This indicates a decay rate of alpha ~ 0.7 (afterglow flux proportional to t^-alpha), which is consistent with early-time UVOT observations (GCN 6336, Immler et al.). We note that there is a source with constant brightness only 1 arcseconds West and 0.7 arcseconds North of the afterglow of GRB 070420. This source has magnitudes I~20 and J~18.5 (magnitudes are calibrated using USNO-B1.0 values in the optical and 2MASS stars in the IR.). The source appears to have a stellar profile and is most likely just a coincident star.