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.)
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.
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