TITLE: GCN CIRCULAR NUMBER: 30161 SUBJECT: GRB 210610A: MITSuME Akeno optical observation DATE: 21/06/10 16:13:57 GMT FROM: Ryohei Hosokawa at Tokyo Institute of Technology R. Hosokawa, K. L. Murata, M. Niwano, N. Ito, H. Takamatsu, Y. Imai, S. Sato, M. Takaku, R. Noto, R. Yamaguchi, Y. Yatsu, and N. Kawai (TokyoTech) report on behalf of the MITSuME collaboration: We observed the field of GRB 210610A (K. L. Page et al. GCN Circular #30160) 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 with a series of 10 sec exposures started at 2021-06-10 15:04:41 UT (58 seconds after Swift BAT trigger). We stacked the images with good conditions. We detected the point source at the position consistent with the afterglow detected previously (K. L. Page et al. GCN Circular #30160) We measured the magnitudes as follows. filter MID-UT T-EXP[sec] measured magnitudes ------------------------------------------------------------------------------------------------ g' 15:08:47 10 16.4+/-0.4 Rc 15:08:29 50 15.3+/-0.1 Ic 15:08:29 50 15.0+/-0.2 ------------------------------------------------------------------------------------------------ T-EXP: Total Exposure time We used PS1 catalog for flux calibration. The magnitudes are expressed in the AB system. The images were processed in real-time through the MITSuME GPU reduction pipeline (Niwano et al. 2021, PASJ, Vol.73, Issue 1, Pages 4-24; https://github.com/MNiwano/Eclaire).