TITLE: GCN CIRCULAR NUMBER: 6553 SUBJECT: GRB 070612B: Optical Observation by MITSuME Akeno DATE: 07/06/18 06:36:27 GMT FROM: Nobuyuki Kawai at Tokyo Tech Y.kudo, T. Ishimura, Y. Yatsu, T. Shimokawabe, N. Vasquez, and N. Kawai (TokyoTech) report on behalf of the MITSuME collaboration: We observed the error box of GRB070612B (Grupe et al., GCN 6511) with the 3-color 50cm MITSuME Telescope at Akeno, Japan starting at 11:46:53 June 12 UT, 5.1 hours after the trigger. In the co-added images of Ic, Rc, and g' bands, we did not detect any new source in the XRT error circle. The 3-sigma limiting magnitudes based on USNO-B1.0 (I-band) and NOMAD (R-band,g'-band) stars are following. Filter start time end time Exp(s) Mag (3-sigma upper limit) ----------------------------------------------------------------- g' 11:46:53 12:16:35 25 x 60s 17.4 Rc 11:46:53 12:16:35 25 x 60s 18.6 Ic 11:46:53 12:16:35 25 x 60s 18.6 -----------------------------------------------------------------