TITLE: GCN CIRCULAR NUMBER: 14418 SUBJECT: GRB 130420A: GMG optical observation DATE: 13/04/20 18:49:21 GMT FROM: Xiao-hong Zhao at Yunnan Obs X.-H. Zhao (YNAO and PSU), J. Mao (RIKEN and YNAO), J.-M. Bai (YNAO) report on behalf of a larger collaboration: We observed the field of GRB 130420A (Page et al., GCN 14406) with 2.4m Gao-Mei-Gu (GMG) telescope. Observations started at 13:36:00 UT on 2013-04-20 (i.e., 6.13 hrs after the burst, ~2 hrs later than the observation of Xu et al., GCN 14413) and 3x600s R-band and 1x600s I-band images were obtained. The optical counterpart of this burst was detected in both bands. The mag are R~19.4 and I~20.2 calibrated with USNO B1 stars. We thank the GMG staff, especially Yu-Xin Xin, Gui-Hua He and Jian-Duo He for performing these observations.