TITLE: GCN CIRCULAR NUMBER: 21124 SUBJECT: GRB 170519A: MITSuME Akeno Optical Observation DATE: 17/05/22 06:07:27 GMT FROM: Taketoshi Yoshii at Tokyo Tech K. Morita, Y. Saito, R. Itoh, T. Yoshii, Y. Tachibana, S. Harita, Y. Muraki, T. Ozawa, K. Shiraishi, H. Mamiya, Y. Yatsu, and N. Kawai (Tokyo Tech) report on behalf of the MITSuME collaboration: We searched for the optical counterpart of GRB 170519A (T. N. Ukwatta et al., GCN Circular #21106) 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 2017-05-19 11:03:14 UT (21192 sec after the burst). We detected the optical counterpart (T. N. Ukwatta et al., GCN Circular #21106) in g', Rc and Ic band. The measured magnitudes were listed as follows. T0+[hour] MID-UT T-EXP[sec] g' Rc Ic ---------------------------------------------------------------------------- ~5.9 11:34:54 4278   19.14+/-0.15 18.48+/-0.11 18.13+/-0.13 ---------------------------------------------------------------------------- T0+ : Elapsed time after the burst T-EXP: Total Exposure time We used GSC2.3 catalog for flux calibration.