TITLE: GCN CIRCULAR NUMBER: 18491 SUBJECT: GRB 151027A: MITSuME Akeno Optical observation DATE: 15/10/27 16:23:13 GMT FROM: Taketoshi Yoshii at Tokyo Tech Y. Yano, T. Yoshii, Y. Saito, Y. Tachibana, H. Ohuchi, S. Kurita, Y. Ono, T. Fujiwara, S. Harita, Y. Muraki, Y. Yatsu, and N. Kawai (Tokyo Tech) report on behalf of the MITSuME collaboration: We observed the field of GRB 151027A (A. Maselli et al., GCN Circular #18478) with the optical three color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50 cm telescope of Akeno Observatory, Yamanashi, Japan. The observation started on 2015-10-27 09:13:52 UT ( 5.25 h after the burst). We detected the previously reported optical afterglow of GRB 151027A (WeiKang Zheng et al., GCN Circular #18479) in the g',Rc and Ic band. The measured magnitudes are listed below. T0+[sec] MID-UT T-EXP[sec] g' Rc Ic ------------------------------------------------------------------------------------------------------------------ 18928 09:34:24 2220 16.72+/-0.06 15.62+/-0.05 16.00+/-0.04 ------------------------------------------------------------------------------------------------------------------ T0+ : Elapsed time after the burst T-EXP: Total Exposure time We used GSC2.3 catalog for flux calibration.