TITLE: GCN CIRCULAR NUMBER: 28697 SUBJECT: GRB 201020A: MITSuME Akeno optical observation DATE: 20/10/20 10:25:22 GMT FROM: Adachi Ryo at Tokyo Institute of Tech R. Adachi, R. Hosokawa, K. L. Murata, 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 201020A (E. Ambrosi et al.,GCN Circular #28696) 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 2020-10-20 08:31:00 UT. The first 28 images were heavily affected by twilight at Akeno Observatory. We detected the point source at the position consistent with the afterglow detected previously (E. Ambrosi et al. GCN #28696). We measured the magnitudes as follows. T0+[min] MID-UT T-EXP[sec] measured magnitudes ------------------------------------------------------------------------------------------------ 196 09:15:39 1260 g'=19.4+/-0.2, Rc=18.4+/-0.1, Ic=18.4+/-0.2 ------------------------------------------------------------------------------------------------ T0+ : Elapsed time after the burst T-EXP: Total Exposure time We used GSC2.3 and 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., accepted for publication in PASJ, https://arxiv.org/abs/2008.11486; https://github.com/MNiwano/Eclaire).