TITLE: GCN CIRCULAR NUMBER: 17340 SUBJECT: GRB 150120B: FTN early optical light curve DATE: 15/01/21 14:51:41 GMT FROM: Cristiano Guidorzi at Ferrara U,Italy C. Guidorzi, S. Dichiara (U. Ferrara), C.G. Mundell (LJMU), A. Gomboc (U. Ljubljana) on behalf of a large collaboration report: The 2-m Faulkes Telescope North observed Swift GRB150120B (D'Elia et al. GCN 17314; Perley GCN 17315) from 18 to 100 minutes since the burst trigger time with SDSS r and i filters. Both light curves are fitted with a power-law with a decay index alpha=0.8 +- 0.1. A comparison with the observations at later times (Perley GCN 17335; Wiseman et al. GCN 17336; Pandey GCN 17337; Xin et al. GCN 17339) suggests that a steepening of the decay must have occurred between ~2e4 and ~6e4 s.