TITLE: GCN CIRCULAR NUMBER: 12733 SUBJECT: GRB 111225A: Keck/LRIS Afterglow Photometry DATE: 11/12/27 06:20:27 GMT FROM: S. Bradley Cenko at Caltech S. B. Cenko, J. S. Bloom, J. M. Silverman, A. N. Morgan (UC Berkeley), D. A. Perley (Caltech), A. Cucchiara, J. X. Prochaska (UCSC / UCO Lick), A. V. Filippenko (UC Berkeley), and P. E. Nugent (LBNL / UC Berkeley) report on behalf of a larger collaboration: We have imaged the field of GRB111225A (Siegel et al., GCN 12720) with the Low-Resolution Imaging Spectrometer (LRIS) mounted on the 10 m Keck I telescope beginning at 4:56 UT on 2012 Dec 26 (~ 25.1 hours after the Swift BAT trigger). We detect the optical afterglow in both the g' and R-band filters, with an approximate magnitude at this time of R ~ 23.2 (estimated uncertainty of 0.3 mag, due largely to preliminary calibration with respect to the USNO-B1 catalog). Compared with previously reported detections (Xin et al, GCN 12725, Gorosabel et al., GCN 12728), this suggests a steep fading of the afterglow emission at this late time (power-index alpha ~ 2.5).