TITLE: GCN CIRCULAR NUMBER: 10726 SUBJECT: GRB 100418A: RTT150 optical observations DATE: 10/05/07 03:44:59 GMT FROM: Irek Khamitov at TUG I. Bikmaev (KSU/AST), I. Khamitov (TUG), N. Sakhibullin (KSU/AST), R. Burenin, M. Pavlinsky, R. Sunyaev (IKI), Z. Eker (TUG), U. Kiziloglu (METU), E. Gogus (Sabanci Uni.) report: The optical afterglow of GRB 100418A (Marshall et al., GCN 10612, Filgas et al., GCN 10617) was observed with Russian-Turkish 1.5-m telescope (RTT150,Bakirlitepe, TUBITAK National Observatory, Turkey) every night during May 1/2 - 6/7, 2010. We obtained 4 - 12 exposures by 900 sec each in Rc filter. Estimates of Rc magnitudes were made relative to the nearby USNO-B1.0 star 1014-0271368 (R2Mag=17.32). Additionally we made 4 x 900 sec exposures in g',r',i' SDSS filters in May 5/6, 2010. OT is still existed in all filters as compared with SDSS host images. We found that OT brightness has decreased from Rc = 21.25 in April 28 (Bikmaev et al., GCN 10700, T+0.792 Ms) to Rc = 21.60 +/- 0.05 in May 5, 2010 (T+1.48 Ms) following a power-law decay with an index of -0.8 +/- 0.1, without plateau reported by Marshall et al. (GCN10720). In May 7, UT(mean) = 0h50m, we estimated Rc = 21.7+/-0.07 mag. It means that OT is began to fade faster after T+1.48 Ms. -- This message has been scanned for viruses and dangerous content by MailScanner, and is believed to be clean.