GCN Circular 31413

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

We observed the field of GRB 220107A (The Fermi GBM team et al. GCN
Circular #31399, F. Kunzweiler et al. GCN Circular #31400, James
DeLaunay et al. GCN Circular #31402, V. Lipunov et al. GCN Circular
#31403, P. A. Evans et al. GCN Circular #31404, P. Veres et al. GCN
Circular #31406, A. Suresh et al. GCN Circular #31408, D.N. Burrows et
al. GCN Circular #31410) 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 was carried out from
2022-01-07 20:21:55 UT (~5.6 hours after the Fermi GBM trigger). We
stacked the images with good conditions.

Our observation covered 100% of the Swift/BAT-GUANO error region
(James DeLaunay et al. GCN Circular #31402). Comparing our co-added
images with the GSC2.3 and PS1 catalog, we marginally detected one
uncatalogued source at RA, Dec = (169.80774, 34.17079), which is
equivalent to:
RA (J2000): 11h19m13.859s
Dec(J2000): +34d 10' 14.845"
This position is 4.4 arcsec from the center of Swift XRT position
(D.N. Burrows et al. GCN Circular #31410).
The magnitudes of the source are as follows.

T0+[hour] | MID-UT | T-EXP[sec] | candidate magnitude | 5-sigma limits
------------------------------------------------------------------------------------------------
5.4 | 2022-01-07 20:55:27 | 1620 | g'=19.8 +/- 0.5, Rc=18.9 +/- 0.2,
Ic=18.3 +/- 0.2 | g'>20.9, Rc>21.0, Ic>20.3
------------------------------------------------------------------------------------------------
T0+ : Elapsed time after the burst
T-EXP: Total Exposure time

We used PS1 catalog for flux calibration. The conversion from PS1 r
and i band to our Rc and Ic band is by the equation of Tonry et al.
(2012), Table. 6. 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).