TITLE: GCN CIRCULAR NUMBER: 23022 SUBJECT: GRB 180721A: MITSuME Akeno optical upper limits DATE: 18/07/23 09:52:13 GMT FROM: Ryosuke Itoh at Tokyo Institute of Tech. M. Oeda, R. Itoh, K. L. Murata, Y. Tachibana, S. Harita, K. Morita, K. Shiraishi, K. Iida, R. Adachi, S. Niwano, Y. Yatsu, and N. Kawai (Tokyo Tech) report on behalf of the MITSuME collaboration: We searched for the optical counterpart of GRB 180721A (B. Sbarufatti et al., GCN Circular #22994) with the optical three color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50cm telescope of Akeno Observatory, Yamanashi, Japan. The observation started on 2018-07-21 13:44:45.05 UT. We did not find any point source at the enhanced position of the XRT error circle (M.R. Goad et al., GCN Circular #22997) in all three bands. We obtained following 5-sigma upper limits for the magnitudes. T0+[min] MID-UT T-EXP[sec] g' Rc Ic ------------------------------------------------------------------------------------------------------- 157.95 14:27:28 4,740 >16.9 >17.3 >16.9 ------------------------------------------------------------------------------------------------------- T0+ : Elapsed time after the burst T-EXP: Total Exposure time We used UCAC-4 catalog for flux calibration.