GCN Circular 29859

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

We observed the field of GRB 210419C (M. J. Moss et al. GCN Circular
#29834, A.P. Beardmore et al. GCN Circular #29839, WeiKang Zheng and Alexei
V. Filippenko report on et al. GCN Circular #29840, Simone Leonini et al.
GCN Circular #29842, Nat Butler et al. GCN Circular #29843, T. Sakamoto et
al. GCN Circular #29856) with the optical three color (g', Rc, and Ic) CCD
cameras attached to the MITSuME 50 cm telescope of Akeno Observatory,
Yamanashi, Japan. The observation with a series of 60 sec exposures started
at 2021-04-20 10:40:08 UT (11.2 hours after the Swift BAT trigger). We
stacked the images with good conditions. We did not detect any sources
within the enhanced XRT error region (A.P. Beardmore et al. GCN Circular
#29839) in all three bands. 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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11.6 11:38 3000 g'>19.6, Rc>19.9, Ic>19.3
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T0+ : Elapsed time after the burst
T-EXP: Total Exposure time
We used the 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).