TITLE: GCN CIRCULAR NUMBER: 22188 SUBJECT: GRB 171205A: LSGT optical afterglow follow-up observation DATE: 17/12/06 13:17:04 GMT FROM: Myungshin Im at Seoul Nat U Changsu Choi, Myungshin Im (CEOU/SNU), on behalf of a larger collaboration We observed the field of GRB 171205A (D'Elia et al., GCN 22177) with SNUCAM-II (Choi & Im 2017, JKAS, 50, 71) on the 0.43m Lee Sang Gak Telescope (LSGT; Im et al. 2015, JKAS, 48. 207) at the Siding Spring Observatory in Australia. The observation started at about 9 hours after the BAT alert, using r, i, z (broad-band), m425, m475, m525, m575, and m625 (medium-band) filters. We clearly identify the optical afterglow in these bands, and preliminary photometry results in r, i, and z filters are reported below. Note that the photometric calibration is based on stars from the Pan-Starrs catalog in the vicinity of GRB 171205A, and systematic errors due to host galaxy subtraction uncertainty could amount to a few tenths of magnitude. Filter Mag err UT(center) r18.0 0.1 2017-12-05T16:17:17 i 18.1 0.1 2017-12-05T16:26:55 z 18.3 0.2 2017-12-05T16:36:33 Further observations and analysis are being carried out.