TITLE: GCN CIRCULAR NUMBER: 9548 SUBJECT: GRB 090618: RTT150 optical observations DATE: 09/06/22 09:50:24 GMT FROM: Rodion Burenin at IKI, Moscow A. Galeev, I. Bikmaev, N. Sakhibullin (KSU/AST), R. Burenin, M. Pavlinsky, R. Sunyaev (IKI), I. Khamitov, Z. Eker (TUG), U. Kiziloglu (METU), E. Gogus (Sabanci Uni.) report: We observed the OT (Schady et al., GCN 9512; Cenko et al., GCN 9513; Perley, GCN 9514; Rujopakarn et al., GCN 9515) of the Swift GRB 090618 with Russian-Turkish 1.5-m telescope (RTT150, Bakirlitepe, TUBITAK National Observatory, Turkey), in BRc bands, starting at 22 Jun, 00:03 UT, i.e. approximately 3.65 days after the burst, using TFOSC. We made 3x900s exposures in Rc band and 2x900 in B band. The OT is detected in all images. Using the same USNO-B1 star as it was used by Rumyantsev and Pozanenko (GCN 9539) we estimate Rc magnitude as m_Rc=21.60+/-0.04 (3.68 days after the burst). The finding chart can be found at: http://hea.iki.rssi.ru/grb/090618/indexeng.html