TITLE: GCN CIRCULAR NUMBER: 21991 SUBJECT: GRB 171010A: LCO 1m telescope observations DATE: 17/10/11 14:17:15 GMT FROM: Cristiano Guidorzi at Ferrara U,Italy C. Guidorzi (U. Ferrara), S. Kobayashi (LJMU), C.G. Mundell (U. Bath), A. Gomboc (U. Nova Gorica), I.A. Steele (LJMU) on behalf of a large collaboration report: We began observing Fermi LAT GRB 171010A (Omodei et al. GCN 21985) on October 11, from 02:15 to 02:28 UT (7.2 hours since the GRB trigger time) with one of the 1-m LCO telescopes in Sutherland in the SDSS-I filter. Within the enhanced Swift-XRT circle (D'Ai et al. GCN 21989) we clearly detect the optical afterglow (Thorstensen and Halpern, GCN 21987; Izzo and Malesani, GCN 21988) with the following magnitude: Mid Time      Exposure       Filter       Magnitude (AB) (hrs)           (s) ------------------------------------------------------- 7.3            5x120         SDSS-I       16.82 +- 0.02 ------------------------------------------------------- as calibrated against nearby Pan-STARRS objects.