TITLE: GCN CIRCULAR NUMBER: 22154 SUBJECT: GRB 171123A: MITSuME Akeno optical upper limits DATE: 17/11/24 07:02:25 GMT FROM: Katsuhiro L. Murata at Nagoya U K. Morita, R. Itoh, K. L. Murata, T. Yoshii, Y. Tachibana, S. Harita, T. Ozawa, H. Mamiya, K. Shiraishi, Y. Yatsu, and N. Kawai (Tokyo Tech) report on behalf of the MITSuME collaboration: We searched for the optical counterpart of GRB 171123A (P. A. Evans et al., GCN Circular #22148) 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 2017-11-23 16:24:30.61 UT. We did not find any new point source within enhanced XRT circle (M.R. Goad et al., GCN Circular #22150) in all three bands. We obtained following limits for the magnitudes. T0+[hour] MID-UT T-EXP[sec] g' Rc Ic ------------------------------------------------------------------------------------------------------- ~3.15 18:56:14.59 9360 >21.1 >20.7 >19.6 ------------------------------------------------------------------------------------------------------- T0+ : Elapsed time after the burst T-EXP: Total Exposure time We used GSC2.3 catalog for flux calibration.