GCN Circular 23617

R. Itoh, K. L. Murata, Y. Tachibana, S. Harita, K. Morita,
K. Shiraishi, 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 190106A (Sonbas et al., GCN
Circular #23615) with the optical three color (g', Rc, and Ic) CCD cameras
attached to the MITSuME 50cm telescope of Akeno Observatory, Yamanashi, Japan.

The observation started on 13:35:33 UT which corresponds to
49 sec after the trigger.
We detected the point source at the position consistent with the Swift/UVOT
observation (Sonbas et al., GCN Circular #23615) and MASTER
observation (Lipunov et al., GCN Circular #23616).
The measured magnitudes are listed as follows.

T0+[sec]    MID-UT      T-EXP[sec]        g'       Rc        Ic
-------------------------------------------------------------------------------------------------------
~49      13:36:02.6           60               ~16.1      ~15.6   ~15.5
-------------------------------------------------------------------------------------------------------
T0+ : Elapsed time after the burst
T-EXP: Total Exposure time
We used UCAC-4 catalog for flux calibration.
The magnitudes are expressed in the AB system.

Further analysis is ongoing.