TITLE: GCN CIRCULAR NUMBER: 15486 SUBJECT: GRB 131031A: Mondy optical observations DATE: 13/11/15 00:06:28 GMT FROM: Alina Volnova at SAI MSU 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 field of the Swift GRB 131031A (Cummings et al., GCN 15421) with AZT-33IK telescope of Sayan observatory (Mondy). We took several images in R-filter of 60 s exposure on Nov., 01, 02, and 05. In the stacked images from Nov. 01 and 02 in the XRT error circle (Gompertz & Page, GCN 15424) we detected a source which is coincident with the source reported by Gorosabel et al. (GCN 15426). The details of the photometry are the following: date UT start t-T0 Filter Exp. OT (mid, days) (s) 20131101 15:50:21 1.23918 R 147x60 22.23 +/- 0.14 20131102 14:59:29 2.17988 R 106x60 22.43 +/- 0.16 20131105 15:59:53 5.21974 R 91x60 >22.3 (UL 3 sigma) The photometry is based 3 SDSS stars, R (gri -> R transformations by Lupton 2005): SDSS id R J015828.04-013339.6 19.230 J015828.59-013429.3 17.299 J015835.16-013313.8 18.742