TITLE: GCN CIRCULAR NUMBER: 10694 SUBJECT: GRB 100418A: Terskol optical observations DATE: 10/04/27 09:50:55 GMT FROM: Alina Volnova at SAI MSU M. Andreev,  A. Sergeev (Terskol Branch of  Institute of Astronomy), A. Volnova (SAI MSU), A. Pozanenko (IKI) report on behalf of larger GRB follow-up collaboration: We observed the field of the Swift GRB 100418A (Marshall et al. GCN 10612) with the Z-600 telescope of Mt.Terskol observatory in R-filter between (UT) Apr. 20 19:47 - 23:00 under good weather conditions with mean seeing of about 1.6 arcsec. The optical afterglow (Marshall et al. GCN 10612, Filgas et al. GCN 10617) is clearly detected in enhanced XRT error circle (Osborne et al. GCN 10614). The photometry of the afterglow in a stacked image based on USNO-B1.0 star 1014-0271368 (RA(J2000) = 17:05:26.42 Dec(J2000)= +11:27:32.9) assuming R=17.32 is following: T0+       Filter,   Exposure,    mag.               UL (mid, d)            (s) 2.0175   R         50x180       19.85 +/- 0.18   20.8