TITLE: GCN CIRCULAR NUMBER: 28713 SUBJECT: GRB 201020A: DOAO optical afterglow observations DATE: 20/10/21 04:51:18 GMT FROM: Gregory SungHak Paek at SNU Gregory S.H. Paek (CEOU/SNU), Myungshin Im (CEOU/SNU), Taewoo Kim, and Wonseok Kang (DOAO) on behalf of a larger collaboration We observed the optical counterpart of GRB 201020A (E. Ambrosi et al., GCN #28696; R. Adachi et al., GCN #28697; J.P. Osborne et al., GCN #28698; V. Lipunov et al., GCN #27800, S.Y. Fu et al., GCN #28701; S. Belkin et al., GCN #28703, T. Pankov et al., GCN #28708, and H. Kumar et al., GCN #28711) with the 1-m class telescope in Deokheung Optical Astronomy Observatory (DOAO). We calibrated flux with PS1 catalog and use AB magnitude system. --------------------------------------------------------------------- Mid Date[UT] Mid t-t0[days] Filter Exp.time[s] Mag Error --------------------------------------------------------------------- 2020-10-20 10:28:07 0.195 V 300*3 19.361 0.059 2020-10-20 10:33:21 0.199 R 300*3 19.006 0.042 2020-10-20 10:38:35 0.202 I 300*3 18.767 0.039 t0 : 2020-10-20 05:47:26 UT (E. Ambrosi et al., GCN #28696) The magnitudes are not corrected for galactic extinction.