TITLE: GCN CIRCULAR NUMBER: 21121 SUBJECT: GRB 170519A: MITSuME Okayama Optical Observation DATE: 17/05/20 05:01:54 GMT FROM: Daisuke Kuroda at OAO/NAOJ D. Kuroda, K. Yanagisawa, Y. Shimizu, H. Toda (OAO, NAOJ), S. Nagayama (NAOJ), M. Yoshida (Subaru, NAOJ), K. Ohta (Kyoto) and N. Kawai(Tokyo Tech) report on behalf of the MITSuME and OISTER collaboration: We observed the field of GRB 170519A (Ukwatta et al., GCNC 21106) with the optical three color (g', Rc and Ic) CCD camera attached to the MITSuME 50cm telescope of Okayama Astrophysical Observatory. The observation started on 2017-05-19 11:03:26 UT (~5.9 h after the burst). We detected the previously reported afterglow (Ukwatta et al., GCNC 21106; Izzo et al., GCNC 21108) in all the three bands. Photometric results of the OT are listed below. We used SDSS-DR8 catalog for flux calibration. #T0+[day] MID-UT T-EXP[sec] g' g'_err Rc Rc_err Ic Ic_err ------------------------------------------------------------------ 0.26646 11:33:44 3120.0 19.1 0.2 18.7 0.2 18.1 0.2 ------------------------------------------------------------------ T0+ : Elapsed time after the burst [day] T-EXP: Total Exposure time [sec]