TITLE: GCN CIRCULAR NUMBER: 29164 SUBJECT: GRB 201223A: MITSuME Akeno optical observation DATE: 20/12/24 02:08:01 GMT FROM: Ryohei Hosokawa at Tokyo Institute of Technology R. Hosokawa, K. L. Murata, R. Adachi, M. Niwano, F. Ogawa, N. Nakamura, N. Ito, S. Ogata, H. Takamatsu, H. Hara, Y. Yatsu, and N. Kawai (TokyoTech) report on behalf of the MITSuME collaboration: We observed the field of GRB 201223A (J.D. Gropp et al., GCN #29158, J. Wood et al., GCN #29161) 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 at 2020-12-23 17:59:18 UT (52s after Swift BAT trigger). We detected the point source at the position consistent with the afterglow detected previously (Lipunov et al. GCN #29157, Gropp et al., GCN #29158, Z.P. Zhu et al. GCN #29159, Y.-D. Hu et al. GCN #29160). We measured the magnitudes as follows. T0+[sec] MID-UT T-EXP[sec] measured magnitudes ------------------------------------------------------------------------------------------------ 52 17:59:48 60 g'=15.45+/-0.05, Rc=15.04+/-0.03, Ic=14.77+/-0.04 ------------------------------------------------------------------------------------------------ T0+ : Elapsed time after the burst 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., https://doi.org/10.1093/pasj/psaa091, https://arxiv.org/abs/2008.11486; https://github.com/MNiwano/Eclaire).