TITLE: GCN CIRCULAR NUMBER: 16185 SUBJECT: GRB 140423A: RTT150 optical observations DATE: 14/04/29 19:47:26 GMT FROM: Rodion Burenin at IKI, Moscow I. Bikmaev (KFU/AST), I. Khamitov (TUG), S. Melnikov, N. Sakhibullin (KFU/AST), R. Burenin, M. Pavlinsky, R. Sunyaev (IKI), H. Kirbiyik (TUG), U. Kiziloglu (METU), E. Gogus (Sabanci Uni.) report: The field of the optical afterglow of GRB 140423A (Sonbas et al., GCN 16142) was observed with Russian-Turkish 1.5-m telescope (RTT150, Bakirlitepe, TUBITAK National Observatory, Turkey) using the TFOSC instrument. We obtained series of 300 sec exposures in B and Rc filters with mean time in April 24, 00:34 UT (B) and April 24, 01:58 UT (Rc). The afterglow is clearly detected in combined images. Using the USNO-B1 (1398-0233739) star at RA = 13:09:13.1, DEC = +49:53:11, with B1_mag = 16.70, R1_mag = 14.76 as a reference, we estimated the B and R-magnitudes of the afterglow: Filter T-T0, hours Mag. +/- Mag.err B 16.03 23.21 +/- 0.09 Rc 17.43 21.29 +/- 0.06