TITLE:   GCN CIRCULAR
NUMBER:  35073
SUBJECT: GRB 231117A: GOTO optical upper limits
DATE:    23/11/17 11:36:55 GMT
FROM:    Ben Gompertz at U of Birmingham <b.gompertz@bham.ac.uk>

B. Godson, K. Ackley, B. P. Gompertz, J. Lyman, M. Dyer, D. Steeghs, A. Kumar, A. J. Levan, R. Starling, F. Jiménez-Ibarra, K. Ulaczyk, D. Galloway, V. Dhillon, P. O'Brien, G. Ramsay, K. Noysena, R. Kotak, R. Breton, L. Nuttall, E. Pallé, D. Pollacco, T. Killestein and D. O'Neill report on behalf of the GOTO collaboration:

The Gravitational-wave Optical Transient Observer (GOTO, Steeghs et al. 2022) performed a targeted observation in response to GRB 231117A (Laha et al., GCN 35071; Navaneeth et al, GCN 35072) at 10:00:02 UT on 2023-11-17, starting approximately 7 hours after trigger. The observation consisted of a 4x90s exposure in the GOTO L-band (400-700 nm).

Images were processed immediately after acquisition using the GOTO pipeline. No optical counterpart to the X-ray afterglow detected by Swift/XRT (Laha et al., GCN 35071) is seen to a 3-sigma limit of L > 20.4 magnitudes (AB).

Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction.

GOTO (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).