TITLE: GCN CIRCULAR NUMBER: 30193 SUBJECT: GRB 210610B: GOTO confirmation of afterglow detection DATE: 21/06/11 08:16:32 GMT FROM: Travis Mong at Monash University Y-L Mong (1); K. Wiersema (2); R. Starling (3); K. Ackley (1); M. Dyer (4); D. K. Galloway (1); J. Lyman (2); K. Ulaczyk (2); D. Steeghs (2); V. Dhillon (4); P. O'Brien (3); G. Ramsay (5); S. Poshyachinda (6); R. Kotak (7); L. Nuttall (8); D. Pollacco (2); R. Breton (9) ((1) Monash University, (2) Warwick University, (3) University of Leicester, (4) University of Sheffield, (5) Armagh Observatory & Planetarium, (6) National Astronomical Research Institute of Thailand, (7) University of Turku, (8) University of Portsmouth, (9) University of Manchester) report on behalf of the GOTO collaboration: We carried out observations with the Gravitational-wave Optical Transient Observer (GOTO) on La Palma in response to GRB 210610B (Page et al; GCN 30170). We detect an uncatalogued source consistent with the OT reported by Swift UVOT (Page et al.; GCN 30170) and other facilities. We made a series of 4x90 s exposures using our wide L-band filter(400-700 nm) beginning around ~4hrs after the trigger, with midtime of the first observation 23:50:18.136 UT on 10 June 2021. We detect an uncatalogued source located at (J2000): RA 16:15:40.369Dec +14:23:57.19 confirming the OT (Page et al.; GCN 30170, Kumar et al.; GCN 30174, Rumyantsev et al.; GCN 30175, 30178, Hu et al.; GCN 30177, de Wet et al.; GCN 30180, Romanov; GCN 30181, Fynbo et al.; GCN 30182, Moskvitin et al.; GCN 30187, Osborne Et al.; GCN 30189, Becerra et al.; GCN 30190). We find an equivalent magnitude of g = (17.86 +/- 0.05) mag based on calibration against PanSTARRS DR1 photometry in ATLAS_REFCAT2 (Tonry et al. 2018). Observations are continuing. GOTO is operated at the La Palma observing facilities of the Universityof Warwick on behalf of a consortium including the University ofWarwick, Monash University, Armagh Observatory, the University ofLeicester, the University of Sheffield, the National AstronomicalResearch Institute of Thailand (NARIT), Turku University, Portsmouth University, Manchester University and the Instituto de Astrofisicade Canarias (IAC) (https://goto-observatory.org)