TITLE: GCN CIRCULAR NUMBER: 22140 SUBJECT: GRB 171120A: MITSuME Akeno optical upper limits DATE: 17/11/21 10:18:12 GMT FROM: Katsuhiro L. Murata at Nagoya U H. Mamiya, R. Itoh, K. L. Murata, T. Yoshii, Y. Tachibana, S. Harita, K. Morita, T. Ozawa, K. Shiraishi, Y. Yatsu, and N. Kawai (Tokyo Tech) report on behalf of the MITSuME collaboration: We searched for the optical counterpart of GRB 171120A (A. Tohuvavohu et al., GCN Circular #22133) with the optical three color (g', Rc, and Ic) CCD cameras attached to the MITSuME 50 cm telescope of Akeno Observatory, Yamanashi, Japan. The observation started on 2017-11-20 15:38:32.17 UT. We did not find any new point source within enhanced XRT circle (P.A. Evans al., GCN Circular #22135) in all three bands. We obtained following limits for the magnitudes. T0+[hour] MID-UT T-EXP[sec] g' Rc Ic ------------------------------------------------------------------------------------------------------ ~3.26 18:40:07.63 9960 >21.5 >20.7 >19.8 ------------------------------------------------------------------------------------------------------ T0+ : Elapsed time after the burst T-EXP: Total Exposure time We used GSC2.3 catalog for flux calibration.