TITLE: GCN CIRCULAR NUMBER: 31418 SUBJECT: GRB 220107B: MITSuME Akeno optical upper limits DATE: 22/01/09 09:54:23 GMT FROM: Masafumi Niwano at Tokyo Institute of Tech M. Niwano, R. Hosokawa, Y. Imai, K. L. Murata, Y. Takamatsu, N. Ito, R. Noto, S. Sato, M. Takaku, R. Yamaguchi, Y. Yatsu, and N. Kawai (TokyoTech) report on behalf of the MITSuME collaboration: We observed the field of GRB 220107B (M. Arimoto et al. GCN Circular #31409, P. A. Evans et al. #31407, J. D. Gropp et al. #31411,  A. Suresh et al. #31412, P. Veres and C. Meegan #31414, S.Q. Jiang et al. #31417) with the optical three color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50 cm telescope Akeno. The observation with a series of 60 sec exposures started at 2022-01-08 17:04:13 UT (22 hours after Fermi trigger). We stacked the images with good conditions. We did not detect any uncatalogued sources within the XRT error region (J. D. Gropp et al. GCN Circular #31411). We obtained the 5-sigma limits of the stacked images as follows. T0+[hours] MID-UT T-EXP[sec] 5-sigma limits ------------------------------------------------------------------------------------------------ 22.0 2022-01-08 18:58:13 11820 g'>20.7, Rc>20.9, Ic>20.1 ------------------------------------------------------------------------------------------------ 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. 2021, PASJ, Vol.73, Issue 1, Pages 4-24; https://github.com/MNiwano/Eclaire).