GCN Circular 22979
I. Reva (FAPHI), A. Pozanenko (IKI), A. Volnova (IKI), E. Mazaeva (IKI), A. Kusakin (FAPHI), M. Krugov (FAPHI) report on behalf of larger GRB follow-up collaboration: We observed the field of GRB 180720B (Siegel et al., GCN 22973) with Zeiss-1000 telescope of Tien Shan Astronomical Observatory starting on July 20 (UT) 19:46:17. We obtained several images in R and B-filters. The optical afterglow (Martone et al. GCN 22976; Sasadaet al., GCN 22977) is clearly detected in both filters. Preliminary photometry of the afterglow at (UT, mid time) 19:59 is R =17.1 +/- 0.1. The photometry is based on nearby USNO-B1.0 (R2) stars.