GCN Circular 30718

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

We observed the field of GRB 210824A (Fermi GBM team, GCN Circular 
#30699, K. L. Page et al. GCN Circular #30700, M.R. Goad et al. GCN 
Circular #30702, V. D'Elia et al. GCN Circular #30704, X. Liu et al. GCN 
Circular #30705, V. Lipunov et al. GCN Circular #30706, S. Lesage et al. 
GCN Circular #30707, Y.-D. Hu et al. GCN Circular #30708, V. Lipunov et 
al. GCN Circular #30709) 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 started at 2021-08-25 
10:20:44 UT (30.1 hours after Fermi trigger). We stacked the images with 
good conditions. We did not detect any uncatalogued sources within the 
XRT error region (V. D'Elia et al. GCN Circular #30706). We obtained the 
5-sigma limits of the stacked images as follows.

T0+[hour] MID-UT T-EXP[sec] 5-sigma limits
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31.3 2021-08-25 12:29:20.71 4740 g'>18.6, Rc>19.0, Ic>18.3
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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).