GCN Circular 30087

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

We observed the field of GRB 210527A (S. Laha et al. GCN Circular
#30081, J.P. Osborne et al. GCN Circular #30082, P.A. Evans et al. GCN
Circular #30083, Nat Butler et al. GCN Circular #30084, V. D'Elia et
al. GCN Circular #30085, V. Lipunov et al. GCN Circular #30086) 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 2021-05-27
10:23:37 UT (3.3 hours after the triggers). We stacked the images with
good conditions. We did not detect any sources within the enhanced XRT
error region (P.A. Evans et al. GCN Circular #30083) 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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3.3 2021-05-27 15:28 1980 g'>18.0, Rc>18.6, Ic>18.1
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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).