TITLE: GCN CIRCULAR NUMBER: 23503 SUBJECT: GRB181201A: GOTO optical observations DATE: 18/12/04 14:09:38 GMT FROM: Danny Steeghs at U.of Warwick/GOTO G.Ramsay (Armagh O.), J.Lyman, K.Ulaczyk, D.Steeghs, K.Wiersema (U. Warwick), M.Dyer (U. Sheffield), B.Gompertz, A.Levan, R.Cutter (U. Warwick) K. Ackley, D.Galloway, E.Rol (Monash U.), V.Dhillon (U. Sheffield), P.O'Brien, R.Starling (U. Leicester), S.Poshyachinda (NARIT), D.Pollacco (U. Warwick), E.Thrane (Monash U.), E.Palle (IAC) report on behalf of the GOTO collaboration: The Gravitational-wave Optical Transient Observer observed the field of the long duration GRB 181201A (Mereghetti et al. GCN Circ. 23469, Page et al. GCN Circ. 23474) from Roque de los Muchachos Observatory. We report two optical photometric detections, both made using a combined L-band image (400-700nm passband), each with a total exposure time of 300s. The resulting preliminary magnitudes are based on a comparison to Panstarrs g-band calibrators and include a systematic error component due to the calibration uncertainty. midpoint time elapsed since burst g 2018-12-01 19:33:18 UT 0.705 days 17.74+/-0.10 mag 2018-12-03 19:41:21 UT 2.711 days 19.48+/-0.15 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/)