TITLE: GCN CIRCULAR NUMBER: 23112 SUBJECT: GRB 180809B: LCO Sutherland observations DATE: 18/08/10 08:59:56 GMT FROM: Cristiano Guidorzi at Ferrara U,Italy C. Guidorzi, R. Martone (U. Ferrara), S. Kobayashi (LJMU), C.G. Mundell (U. Bath), A. Gomboc (U. Nova Gorica), I.A. Steele (LJMU), A. Cucchiara, D. Morris (U. of Virgin Islands) on behalf of a large collaboration report: We observed Swift GRB 180809B (Moss et al. GCN 23105) with the LCO 1-m units at Sutherland Observatory (South Africa) on August 09, from 20:58 to 22:29 UT (corresponding to 0.5 to 2.0 hours from the GRB trigger time) with the SDSS r' and i' filters. We clearly detect the optical afterglow (Moss et al; Lipunov et al. GCN 23109; Watson et al. GCN 23110; Schweyer et al. GCN 23111) in both filters with the following magnitudes: Mid time from GRB      Exposure         Filter Magnitude trigger time (hrs)     (s) --------------------------------------------------------------------- 0.55                   5x60             SDSS r'         19.54 +- 0.08 0.70                   5x60             SDSS i'         19.24 +- 0.07 --------------------------------------------------------------------- as calibrated against nearby Pan-STARRS objects.