TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4652 SUBJECT: GRB 060203: RTT150 optical observations DATE: 06/02/04 07:39:42 GMT FROM: Irek Khamitov at TUG I. Bikmaev, A.Galeev, N. Sakhibullin (KSU/AST) I. Khamitov, Z. Aslan (TUG), U. Kiziloglu (METU), E. Gogus (Sabanci Uni.), R. Burenin, M. Pavlinsky, R. Sunyaev (IKI) report: The field of XRT position of GRB 060203 (Swift BAT Trigger 180151, Retter et al., GCN 4641, GCN 4644) was observed with Russian-Turkish 1.5-m telescope (RTT150, Bakyrlytepe, TUBITAK National Observatory, Turkey) by using Andor CCD. We made series of 30 sec exposures in Rc and V filters, and series of 60 sec exposures in B-filter on February 04, 00:20 - 03:50 UT. We confirm the presence of the fading optical transient found by Malesani et al. (GCN 4645) and Genko et al. (GCN 4646) and estimate its magnitudes (relative to R = 18.1, V = 18.7, and B = 19.6 of nearby USNO star U1575_02633321) on our co-added frames as follows: Rc = 19.9 +-0.1 UT(mean) = 00:49 ( 54 min after the burst) V = 22.3 +-0.3 UT(mean) = 01:33 ( 98 min ) B > 23 UT(mean) = 02:07 ( 2h 12 min) Rc = 21.0 +-0.1 UT(mean) = 02:49 ( 2h 54 min) V > 22.5 UT(mean) = 03:05 ( 3h 10 min) By using our and published R magnitudes the estimated power law decay slope is -0.90+/-0.04 (http://www.tug.tubitak.gov.tr/~irekk/grb/grb060203/grb060203.jpg) The red spectrum of OT is supporting also by IR data of Bloom et al. (GCN 4648). This message may be cited.