TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4180 SUBJECT: GRB 051021A: RTT150 optical observations DATE: 05/10/30 06:41:30 GMT FROM: Rodion Burenin at IKI, Moscow R. Burenin, D. Denisenko, M. Pavlinsky, R. Sunyaev (IKI), I. Khamitov, Z. Aslan (TUG), U. Kiziloglu (METU), E. Gogus (Sabanci Uni.), I. Bikmaev, N. Sakhibullin (KSU/AST) report: The optical transient associated with GRB 051021A (Yoshida et al., GCN 4116; Fox et al., GCN 4120) was observed with Russian-Turkish 1.5-m telescope (RTT150, Bakyrlytepe, TUBITAK National Observatory, Turkey) in BVR filter set, starting at Oct. 21, 18:15 UT, 4.88 hours after the burst. Compared to USNOB, the magnitudes are about: t-t0,h 5.34 R=21.1 9.95 R=21.8 5.70 V=22.2 10.18 V=22.6 In B the object was detected only marginally. This message may be cited.