TITLE: GCN CIRCULAR NUMBER: 10634 SUBJECT: GRB 100418A: optical observations DATE: 10/04/20 15:55:58 GMT FROM: Alexei Pozanenko at IKI, Moscow V. Rumyantsev, D. Shakhovkoy (CrAO), 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 AZT-11 telescope of CrAO between (UT) Apr. 19 01:26 -- 01:54 under poor seeing of about 4 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 coordinates of the afterglow are (J2000) RA= 17:05:27.08 Dec= +11:27:42.3 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. (mid, d) (s) 0.1883 R 9x180 18.54 +/-0.03 A finding char can be found at http://grb.rssi.ru/GRB100418A/GRB100418a_100418_R_azt11.gif