GRB 201223A: MITSuME Akeno optical observation

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).