TITLE: GCN CIRCULAR NUMBER: 34841 SUBJECT: GRB 231017A: GOTO optical upper limits DATE: 23/10/19 16:24:59 GMT FROM: Ben Gompertz at U of Birmingham <b.gompertz@bham.ac.uk> S. Belkin; K. Ackley; A. Kumar; B. P. Gompertz; B. Godson; R. Starling; M. J. Dyer; J. Lyman; K. Ulaczyk; F. Jimenez-Ibarra; D. O'Neill; D. Steeghs; D. K. Galloway; V. Dhillon; P. O'Brien; G. Ramsay; K. Noysena; R. Kotak; R. P. Breton; L. K. Nuttall; E. Pall'e and D. Pollacco report on behalf of the GOTO collaboration: We report on observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022) in response to GRB 231017A (Fermi GBM team, GCN 34822). Targeted observations were performed between 00:20:50 UT on 2023-10-18 and 02:37:04 UT on 2023-10-18 (starting ~16.25 hours after trigger). Each observation consisted of 4x90s exposures in the GOTO L-band (400-700 nm). We identify no candidate optical counterparts within the Swift/BAT-GUANO localisation region (DeLaunay et al., GCN 34824) or at the positions of the 9 sources identified in XRT pointed observations (Evans et al., GCN 34825; Dichiara et al., GCN 34829). The mean 5-sigma limiting magnitude was L > 20.2 mag. This result is consistent with other observations (​​Kumar et al., GCN 34833; Strausbaugh et al., GCN 34834; Shrestha et al., GCN 34836; Xu et al., GCN 34840). Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction. GOTO (https://goto-observatory.org<https://goto-observatory.org/>) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester and the Instituto de Astrofisica de Canarias (IAC). View this GCN Circular online at https://gcn.nasa.gov/circulars/34841. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...