TITLE: GCN CIRCULAR NUMBER: 22950 SUBJECT: GRB 180715A: GOTO optical limits DATE: 18/07/15 23:27:04 GMT FROM: Joe Lyman at U of Warwick J.Lyman, D.Steeghs (U. Warwick), G.Ramsay (Armagh O.), M.Dyer (U. Sheffield), K.Ulaczyk, B.Gompertz, A.Levan, R.Cutter (U. Warwick) K. Ackley, D.Galloway, E.Rol (Monash U.), V.Dhillon (U. Sheffield), P.O'Brien, N.Tanvir (U. Leicester), S.Poshyachinda (NARIT), D.Pollacco (U. Warwick), E.Thrane (Monash U.) report on behalf of the GOTO collaboration: In response to GRB 180715A (Ukwatta et al. GCN 22947), the Gravitational-wave Optical Transient Observer (GOTO) observed the field near the Swift BAT detection. Observations started at 2018-07-15T22:37:10 UT (4.5 hours after the burst) consisted of a set of 3x120s exposures in our wide L filter (400-700nm). We detect the source identified by Guidorzi et al. (GCN 22949) but note that this source appears in PanSTARRS images of the field and in the Gaia catalogue and is thus likely to be unrelated. We did not detect any other uncatalogued source within the BAT localisation uncertainty. A preliminary analysis of the stacked image was used to derive a 5-sigma upper limit of V>20.5 mag. GOTO is operated at the La Palma observing facilities of the University of Warwick on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT) and the Instituto de Astrofisica de Canarias (IAC) https://goto-observatory.org/