TITLE: GCN CIRCULAR NUMBER: 23778 SUBJECT: GRB190123A: MITSuME Akeno optical upper limits DATE: 19/01/24 10:11:22 GMT FROM: Kazuki Shiraishi at Tokyo Institute of Technology K. Shiraishi, K. L. Murata, R. Itoh, Y. Tachibana, S. Harita, K. Morita, K. Iida, M. Niwano, R. Adachi, M. Oeda, Y. Yatsu, and N. Kawai (Tokyo Tech) report on behalf of the MITSuME collaboration We searched for the optical counterpart of GRB 190123A (A. D'Ai et al., GCN #23769) with the optical three color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50 cm telescope at Akeno Observatory,Yamanashi, Japan. The observation started on 12:20:56 UT which corresponds to 103 sec after the trigger. We did not find any new point source within the enhanced XRT circle D’Ai et al., GCN #23769; A.P. Beardmore et al., GCN #23771) in all three bands. We obtained following 5 sigma limits for the magnitudes. T0+[sec] MID-UT T-EXP[sec] g' Rc Ic ------------------------------------------------------------------------------------------------------- 103 12:25:31 540 >18.2 >17.8 >17.0 723 12:35:51 540 >17.9 >17.7 >17.6 1,764 14:21:35 10,800 >18.4 >18.2 >17.4 ------------------------------------------------------------------------------------------------------- T0+ : Elapsed time after the burst T-EXP: Total Exposure time We used UCAC-4 catalog for flux calibration.