TITLE: GCN CIRCULAR NUMBER: 27834 SUBJECT: GRB 200528A: MITSuME Akeno optical upper limits DATE: 20/05/28 13:14:26 GMT FROM: Adachi Ryo at Tokyo Institute of Tech R. Adachi, R. Hosokawa, K. L. Murata, M. Niwano, F. Ogawa, N. Nakamura, Y. Yatsu, and N. Kawai (Tokyo Tech) report on behalf of the MITSuME collaboration: We observed the field of GRB 200528A (Fermi GBM team, GCN #27831; Ambrosi et al., GCN #27832) with the optical three color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50 cm telescopes of Akeno Observatory in Japan. The observation started on 10:28:31.87 UT. The first 40 images were heavily affected by twilight and bad weather at Akeno Observatory. We checked single images and combined images. We did not find any new point sources within the Swift/XRT error circle (Ambrosi et al., GCN #27832) in all three bands. Also, we did not detect the potential host galaxy (de Ugarte Postigo et al., GCN #27833) due to shallow upper limits of our observation. We obtained the 5-sigma limits as follows. T0+[min] MID-UT T-EXP[sec] 5-sigma limits ------------------------------------------------------------------------------------------------ 36.7 11:28:34 1020 g'>18.9, Rc>18.3, Ic>17.4 ------------------------------------------------------------------------------------------------ T0+ : Elapsed time after the burst T-EXP: Total Exposure time We used the UCAC4 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., submitted; https://github.com/MNiwano/Eclair).