GCN Circular 32883

M. Niwano, R. Hosokawa, I.Takahashi, K. L. Murata, Y. Imai, N. Ito, S. 
Sato, N. Higuchi, M. Tateda, M. Sasada, Y. Yatsu, and N. Kawai (Tokyo 
Tech) report on behalf of the MITSuME collaboration:

We observed the field of GRB 221028A (A. Y. Lien et al. GCN Circular 
#32874, H. Kumar et al. GCN Circular #32876, Y.-D. Hu et al. GCN 
Circular #32878, V. Lipunov et al. GCN Circular #32879, R. Strausbaugh 
et al. GCN Circular #32881) with the optical three color (g', Rc, and 
Ic) CCD cameras attached to the MITSuME 50 cm telescope Okayama.

The observation with a series of 60 sec exposures started at 2022-10-28 
13:17:23 UT (59 seconds after the Swift/BAT trigger). We stacked the 
images with good conditions. We did not detect any uncatalogued sources 
within the Swift/XRT error region (A. Y. Lien et al. GCN Circular 
#32874). We obtained the 5-sigma limits of the stacked images as follows.

T0+[sec] | MID-UT | T-EXP[sec] | 5-sigma limits
------------------------------------------------------------------------------------------------
59 | 2022-10-28 14:17:10 | 5790.0 | g'>18.7, Rc>19.5, Ic>18.7
------------------------------------------------------------------------------------------------
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).