TITLE: GCN CIRCULAR NUMBER: 30825 SUBJECT: GRB 210912A: Mondy optical afterglow confirmation DATE: 21/09/12 17:21:48 GMT FROM: Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru> N. Pankov (HSE), S. Belkin (IKI), A. Pozanenko (IKI), E. Klunko (ISTP) report on behalf of GRB IKI FuN: We observed the field of GRB 210912A (Troja et al., GCN 30820) with AZT-33IK telescope of Sayan observatory (Mondy) starting on 2021-09-12(UT) 12:57:48. We obtained 30 images in R-filter. We confirm the fading object suggested by Hu et al. (GCN 30823) as the optic afterglow of GRB 210912A. Preliminary photometry of the object in stacked images is following Date UT start t-T0 Filter Exp. OT Err. UL(3sigma) (mid, days) (s) 2021-09-12 12:57:48 0.10112 R 29*120 21.33 0.14 22.5 The photometry is based on the nearby USNO-B1.0 stars RA DEC R2 08:39:12.26208 +79:12:37.1304 15.88 08:39:10.94880 +79:16:33.8916 15.26