TITLE: GCN CIRCULAR NUMBER: 20314 SUBJECT: GRB 161219B: MITSuME Akeno Optical Observation DATE: 16/12/21 05:31:31 GMT FROM: Taketoshi Yoshii at Tokyo Tech T.Fujiwara, Y.Saito, Y. Tachibana, T. Yoshii, Y.Ono, S.Harita, Y.Muraki, K.Morita, T.Ozawa, K.Saisho,Y. Yatsu, and N. Kawai (Tokyo Tech) report on behalf of the MITSuME collaboration: We searched for the optical counterpart of GRB 161219B (A. D'Ai et al., GCN Circular #20296) 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 2016-12-20 11:49:20 UT (~17.0 hour after the burst) and we detected the optical counterpart in g', Rc and Ic band. The measured magnitudes were listed as follows. We obtained following results for the magnitudes. T0+[hour] MID-UT T-EXP[sec] g' Rc Ic ------------------------------------------------------------------------------------------------------- ~17.8 12:34:26 4920 18.83 +/- 0.11 18.23 +/- 0.09 18.14 +/- 0.11 ------------------------------------------------------------------------------------------------------- T0+ : Elapsed time after the burst T-EXP: Total Exposure time We used GSC2.3 catalog for flux calibration.