TITLE: GCN CIRCULAR NUMBER: 11190 SUBJECT: GRB 100901A: Kanata Telescope observation of the optical afterglow DATE: 10/09/03 06:03:58 GMT FROM: Michitoshi Yoshida at Okayama Astrophysical Obs M. Yoshida, M. Sasada, T. Komatsu and K. S. Kawabata (HASC, Hiroshima University) We performed R band imaging observation of the optical afterglow of GRB 100901A (Immler et al., GCN 11159) with the 1.5m Kanata telescope of Hiroshima University. The observation was made from 2010-09-02 15:07:24 UT (~1.06 day after the burst) to 15:50:33 UT. The previously reported afterglow (e.g Immler et al. GCN 11159; Kuroda et al. GCN 11172; or Kann et al. GCN 11187) was clearly detected. The afterglow showed a marginal increasing trend in brightness within this observation. Photometric results of the afterglow are listed below. We used USNO- B1.0 1127-0027231 (R = 15.37) for flux calibration. #T0+[day] MID-UT T-EXP[sec] Rc err ----------------------------------------------- 1.070266 15:15:21 900.0 18.62 0.10 1.081620 15:31:42 900.0 18.60 0.07 1.096759 15:53:30 900.0 18.54 0.04 ----------------------------------------------- T0+ : Elapsed time after the burst [day] T-EXP: Total Exposure time [sec]