TITLE: GCN CIRCULAR NUMBER: 26597 SUBJECT: GRB 191227A: MITSuME Akeno optical upper limits DATE: 19/12/27 10:31:08 GMT FROM: Adachi Ryo at Tokyo Institute of Tech R. Adachi, K. L. Murata, M. Oeda, K.Shiraishi, K. Iida, M. Niwano, F. Ogawa, R. Hosokawa, S. Toma, N. Nakamura, Y. Yatsu, and N. Kawai (TokyoTech) report on behalf of the MITSuME collaboration: We observed the field of the optical counterpart (V. Lipunov et al. #26596) of GRB 191227A (The Fermi GBM team #26593, A. Melandri et al. #26595) 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 19/12/27 08:08:42.73 UT. We did not detect the optical counterpart in all three bands. We obtained the following 5-sigma limits for the magnitudes. T0+[hour] MID-UT T-EXP[sec] 5-sigma limits ----------------------------------------------------------------------------------------------------- ~6.75 08:57:46.67 3360 g’>17.4, Rc>16.9, Ic>16.2 ----------------------------------------------------------------------------------------------------- T0+ : Elapsed time after the burst T-EXP: Total Exposure time We used UCAC4 catalog for flux calibration. The magnitudes are expressed in the AB system.