TITLE: GCN CIRCULAR NUMBER: 7026 SUBJECT: GRB 071020: MITSuME Akeno optical observations DATE: 07/10/31 11:38:14 GMT FROM: Nobuyuki Kawai at Tokyo Tech T. Ishimura, Y. Yatsu, T. Shimokawabe, N. Kawai (Tokyo Tech) and M. Yoshida (NAOJ) report on behalf of the MITSuME collaboration: We observed the field of GRB 071020 (Holland et al. , GCN6949) with the 3-color 50cm MITSuME Telescope at Akeno, Japan from UT 16:21 to UT 19:53 on Oct. 20, 9.3 hours after the trigger. In the co-added images of Ic and Rc bands, we detected the optical afterglow reported by Schaefer et al. (GCN 6948). Photometric calibration was done using the USNO-B1.0 (Ic-band) and NOMAD (g'- and Rc-bands) catalogs. The results are following: Filter start end Exposure Mag ------------------------------------------------------ g' 16:21:13 19:53:55 149 x 60s >21.1 (3 sigma upper limit) Rc 16:21:13 19:53:55 149 x 60s 21.2 +/- 0.3 Ic 16:21:13 19:53:55 149 x 60s 19.8 +/- 0.3 ------------------------------------------------------