TITLE: GCN CIRCULAR NUMBER: 20107 SUBJECT: GRB 161023A: LCOGT-FTS optical observations DATE: 16/10/24 10:30:23 GMT FROM: Cristiano Guidorzi at Ferrara U,Italy C. Guidorzi (U. Ferrara), S. Kobayashi, I.A. Steele (LJMU), C.G. Mundell (U. Bath), A. Gomboc (U. Nova Gorica) on behalf of a large collaboration report: The 2-m LCOGT Faulkes Telescope South began observing INTEGRAL GRB 161023A (Mereghetti et al., GCN 20103) in the SDSS ri filters on October 24, 09:17 UT (~0.44 days since the GRB). We clearly detect the optical afterglow (Gorbovskoy et al. GCN 20102; Tanvir al. GCN 20104) at the position RA(J2000)= 20:44:05.17, DEC(J2000)= -47:39:47.8 (error radius of 1 arcsec) with the following values: Mid time from GRB Exposure Filter Magnitude (days) (s) ------------------------------------------------------------- 0.44 5x60 SDSS-R 18.57 +- 0.03 0.45 5x60 SDSS-I 18.38 +- 0.03 ------------------------------------------------------------- Calibration is done against nearby USNOB-1 star 20:44:08.421, -47:39:34.63 assuming r=17.27, i=17.20 mag.