TITLE: GCN CIRCULAR NUMBER: 10695 SUBJECT: GRB 100423A: CrAO optical observations DATE: 10/04/27 09:52:28 GMT FROM: Alina Volnova at SAI MSU V. Rumyantsev, D. Shakhovskoy (CrAO), A. Volnova (SAI MSU), A. Pozanenko (IKI) report on behalf of larger GRB follow-up collaboration: We observed the field of the Swift GRB 100423A (Stroh et al., GCN 10651) with AZT-11 telescope of CrAO Observatory between (UT) Apr. 23 18:15 - 18:46. We do not detect source at the position of the afterglow (Filgas et al., GCN 10652; Ivarsen et al., GCN 10653). The upper limit of the stacked image based on USNO-B1.0 star 1115-0180143 (RA(J2000) = 09 05 44.73 Dec(J2000)= +21 31 14.0) and assuming R=17.21 is following: T0+ Filter, Exposure, mag. (mid, d) (s) 0.7489 R 11x180 >20.7 The upper limit is compatible with power-law decay index -1.1 reported by Ivarsen et al. (GCN 10653).