TITLE: GCN GRB OBSERVATION REPORT NUMBER: 3539 SUBJECT: GRB 050607: RTT150 optical observations DATE: 05/06/08 15:22:37 GMT FROM: Rodion Burenin at IKI, Moscow R. Zhuchkov, I. Bikmaev, N. Sakhibullin (KSU/AST), R. Burenin, M. Pavlinsky, R. Sunyaev (IKI), Z. Aslan, I. Khamitov (TUG), U. Kiziloglu (METU), A. Alpar (Sabanci Uni.) report: We observed the error box of GRB 050607 (Retter et al., GCN 3525) with Russian-Turkish 1.5-m telescope (RTT150, Bakyrlytepe, TUBITAK National Observatory, Turkey). We made a set of 600s exposures in R and I, starting at 21:00 UT, June 07, i.e. approximately 12 hours after the burst. Observations were made under poor weather conditions (with 1.7'' seeing and cirruses). We detect nothing at the position of the OT found by Rhoads et al. (GCN 3527, 3531). The upper limits are approximately I=22.6 and R=23.7. Comparing to earlier measurements (Rhoads et al., GCN 3531) we confirm that the source is fading. This message may be cited.