TITLE: GCN CIRCULAR NUMBER: 28870 SUBJECT: GRB 201104B: MITSuME Akeno optical observation DATE: 20/11/09 09:47:55 GMT FROM: Ryohei Hosokawa at Tokyo Institute of Technology R. Hosokawa, R. Adachi, 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 201104B (B. Sbarufatti et al., GCN #28825) 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 60 sec exposures started at 2020-11-05 08:14:33 UT. The first 29 images were heavily affected by twilight at Akeno Observatory. We marginally detected the point source at the position consistent with the afterglow detected previously (Marshall et al., GCN #28827, Vielfaure et al., GCN #28840, Oates et al., GCN #28851, Belkin et al., GCN #28852, Belkin et al., GCN #28856, and Gupta et al., GCN #28860). We measured the magnitudes as follows. T0+[hour] MID-UT T-EXP[sec] measured magnitudes ------------------------------------------------------------------------------------------------ 15.2 2020-11-05 12:59:59 21360 g'=21.5+/-0.3, Rc=20.7+/-0.2, Ic=20.3+/-0.3 ------------------------------------------------------------------------------------------------ T0+ : Elapsed time after the burst T-EXP: Total Exposure time We used the 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).