TITLE: GCN CIRCULAR NUMBER: 9956 SUBJECT: GRB 090927: Zadko Telescope observations DATE: 09/09/27 20:29:05 GMT FROM: Alain Klotz at CESR-CNRS A. Klotz, T.P. Vaalsta, Liang Yan, and J. Zadko report on behalf of the Zadko Telescope Team. A. Klotz (CESR, OHP), T.P. Vaalsta, Liang Yan, J. Zadko, H. Miao, J. Moore, K. Frost, D. Coward, A. Imerito, D. Blair, R. Burman, P. Luckas, S. Gordon, A. Fletcher, A. Ahmet, (University of Western Australia) M. Todd, M. Zadnik (Curtin University) M. Boer, M. Laas (OHP), P. Thierry (Airbus) The 1.0m F/4 Zadko telescope started imaging the field of GRB 090927 (trigger=370846, Grupe et al., GCN 9945) 110 minutes after the Swift trigger. A fading source was found within the XRT error circle (GCN 9946, Gronwall et al.). The field was observed for 50 minutes using a preliminary version of a robotic observation mode. Preliminary photometry of unfiltered images taken with an iKon DW436BV camera show the following initial magnitudes of the optical afterglow: tmid(min) Exp. Time R Magnitude ------------------------------------- 110 42s >16 126 540s 19.8 +/- 0.5 158 360s 20.0 +/- 0.5 The fading seems to have low decay which is encouraging to perform spectrocopy in the next hours.