TITLE: GCN CIRCULAR NUMBER: 11249 SUBJECT: GRB100906A: Optical observations at IAO DATE: 10/09/07 08:42:23 GMT FROM: Daisuke Kuroda at OAO/NAOJ D. Kuroda (OAO, NAOJ), H. Hanayama, T. Miyaji, J. Watanabe (IAO, NAOJ), K. Yanagisawa (OAO, NAOJ), M. Yoshida (Hiroshima), K. Ohta (Kyoto) and N. Kawai(Tokyo Tech) report on behalf of the MITSuME collaboration: We observed the field of GRB 100906A (Markwardt et al., GCN 11227) with the optical three color (g', Rc and Ic) CCD camera attached to the Murikabushi 1m telescope of Ishigakijima Astronomical Observatory. The observation started on 2010-09-06 17:20:53 UT (~3.5 h after the burst). We detected the previously reported afterglow (Markwardt et al., GCN 11227; Ivanov et al., GCN 11228; Melandri et al., GCN 12229) in all the three bands. Photometric results of the OT are listed below. We used GSC2.3 catalog for flux calibration. #T0+[day] MID-UT T-EXP[sec] g' g'_err Rc Rc_err Ic Ic_err ---------------------------------------------------------------------- 0.15249 17:29:02 840.0 19.3 0.1 18.3 0.1 17.6 0.1 ---------------------------------------------------------------------- T0+ : Elapsed time after the burst [day] T-EXP: Total Exposure time [sec]