Аннотация:AT 2020oj MASTER GCN 26658, GCN 26660 MASTER-SAAO auto-detection system ( Lipunov et al., “MASTER Global Robotic Net”, Advances in Astronomy, 2010, 30L ) discovered gamma-ray burst optical counterpart at (RA, Dec) = 07h 07m 37.66s -83d 43m 06.1s on 2020-01-07.83383 UT (Lipunov et al. GCN 26658, GCN 26660) during MASTER alert observations https://master.sai.msu.ru/site/master2/event.php?id=1253639 of Fermi GBM (GCN 26659) and Swift (GCN 26661) GRB 200107.81/GRB 200107B . This OT is inside 21.3arcsec of Swift XRT error-box (Bernardini et al. GCN 26661) The OT changes, for example unfiltered magnitude m=17.3m at 2020-01-07.83383UT, m=17.9 at 2020-01-07.84459 UT. The OT is seen in 16 images.