GCN Circular 31474

N. Ito, R. Hosokawa, K. L. Murata, M. Niwano, Y. Imai, Y. Takamatsu, R.
Yamaguchi, R. Noto, S. Sato, M. Takaku, Y. Yatsu, and N. Kawai (Tokyo Tech)
report on behalf of the MITSuME collaboration:

We observed the field of GRB 220117B (A. Melandri et al. GCN Circular
#31468, V. Lipunov et al. GCN Circular #31469) with the optical three color
(g', Rc, and Ic) CCD cameras attached to the MITSuME 50 cm telescope Akeno.
The observation started at 2022-01-17 20:06:58 UT (1.5 minutes after Swift
trigger). We stacked the images with good conditions. We did not detect any
sources within the XRT error region (A. Melandri et al. GCN Circular
#31468). We obtained the 5-sigma limits of the stacked images as follows.

T0+[minutes] MID-UT T-EXP[sec] 5-sigma limits
------------------------------------------------------------------------------------------------
2.9 2022-01-17 20:08:19 80 g'>16.3, Rc>16.4, Ic>15.8
28.7 2022-01-17 20:34:10 2280 g'>16.5, Rc>17.0, Ic>16.5
------------------------------------------------------------------------------------------------
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).