TITLE: GCN CIRCULAR NUMBER: 27583 SUBJECT: GRB 200412B: Mondy optical observations DATE: 20/04/15 10:11:58 GMT FROM: Alexei Pozanenko at IKI, Moscow S. Belkin (IKI), A. Pozanenko (IKI), E. Klunko (ISTP), M. Eselevich (ISTP), E. Mazaeva (IKI), A. Volnova (IKI) report on behalf of IKI-GRB FuN: We observed the field of GRB 200412B (Fermi GBM team, GCN 27547; Mailyan et al., GCN 27558; see also Burgess et al., GCN 27548; Longo et al., GCN 27557; Page et al., GCN 27561; Gupta et al., GCN 27563; Zheng et al., GCN 27565) with AZT-33IK 1.5-m telescope of Sayan observatory (Mondy) starting on 2020-04-14 (UT) 14:24:54. We clearly detected the afterglow of GRB 200412B (Lipunov et al., GCNs 27555, 27556; see also Kumar et al., GCN 27564; Belkin et al., GCN 27566, Stecklum et al., GCN 27567, Moskvitin GCN 27570; Xin et al., GCN 27571). Preliminary photometry of the afterglow is following. Date UT start t-T0 Filter Exp. OT Err. UL (mid, days) (s) 2020-04-14 14:24:54 2.23002 R 15*120 21.22 0.08 22.8 The photometry is based on nearby USNO-B1.0 stars UUSNO-B1.0_id R2 1525-0302108 17.21 1524-0300914 17.20 1525-0301929 17.85