GRB 210527A: MITSuME Akeno optical upper limits

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 ------------------------------------------------------------------------------------------------ 3.3 2021-05-27 15:28 1980 g'>18.0, Rc>18.6, Ic>18.1 ------------------------------------------------------------------------------------------------ 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).