GCN Circular 27834

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).