Swift GRB201223.75: Global MASTER-Net OT detection

MASTER-Tavrida robotic telescope (Global MASTER-Net: http://observ.pereplet.ru, Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L) located in Russia (Lomonosov MSU, SAI Crimea astronomical station) was pointed to the GRB201223.75 35 sec after notice time and 51 sec after trigger time at 2020-12-23 17:59:18 UT. On our first (180s exposure) set we found 1 optical transient within Swift error-box (ra=132.846 dec=71.1739 r=0.05) brighter than 18.1. T-Tmid Date Time Expt. Ra Dec Mag ---------|---------------------|-------|-----------------|-----------------|------- 141 2020-12-23 17:59:18 180 ( 8h 51m 09.2s , +71d 10m 47.8s) 15.2 The 5-sigma upper limit has been about 18.1mag The message may be cited.