TITLE: GCN CIRCULAR NUMBER: 16247 SUBJECT: GRB 140423A: Mondy optical observations DATE: 14/05/12 17:32:49 GMT FROM: Alexei Pozanenko at IKI, Moscow A. Volnova (IKI), E. Klunko (ISTP), M. Eselevich (ISTP), I. Korobtsev (ISTP), A. Pozanenko (IKI) report on behalf of larger GRB follow-up collaboration: We observed the optical afterglow (Elenin et al., GCN 16143; Kaur et al., GCN 16144; Ferrante et al., GCN 16145; Chester et al., GCN 16147; Maehara et al., GCN 16151) of the Swift GRB 140423A (Sonbas et al., GCN 16142) with AZT-33IK telescope of Sayan observatory (Mondy). We took several images in R-filter of 60 s exposure on Apr., 25 and of 120 s exposure on Apr., 26 and 27. The details of the photometry are the following: date UT start t-T0 Filter Exp. OT (mid, days) (s) 2014-04-25 16:36:21 2.36772 R 90*60 22.63+/-0.10 2014-04-26 15:56:26 3.34068 R 46*120 23.46+/-0.18 2014-04-27 14:15:32 4.27964 R 54*120 > 22.9 The photometry is based on two SDSS stars, R (gri -> R transformations by Lupton 2005): SDSS id R J130911.04+494854.6 20.209+/-0.053 J130924.79+494946.6 19.533+/-0.038