GCN Circular 14413
D. Xu (DARK/NBI), C. Cao, S.M. Hu (SDU) report: We observed the field of GRB 130420A (Page et al., GCN 14406) using the 1m telescope located in Weihai, Shandong Province, China. Observations started at 11:41:32 UT, 2013-04-20 (i.e., 4.218 hr after the BAT trigger) and 12x180s I-band frames were obtained. The optical afterglow (Page et al., GCN 14406) is clearly detected in our stacked image to be of I=19.4 mag, calibrated with nearby USNO B1 stars. It has decayed by about 0.5 mag, compared to the measurement in Watson et al. (GCN 14409). We thank Dayong Ren for carrying out these observations.