TITLE: GCN CIRCULAR NUMBER: 41048 SUBJECT: EP/WXT 01709181970: GOTO observations confirm stellar variability DATE: 25/07/09 08:35:58 GMT FROM: Amit Kumar at Royal Holloway - UoL/ U of Warwick, UK amitkundu515@gmail.com
A. Kumar, D. O'Neill, G. Ramsay, B. P. Gompertz, R. Starling, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, B. Godson, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, and J. Casares report on behalf of the GOTO collaboration:
We report on observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to EP/WXT trigger ID 01709181970 (Peng et al. GCN 41045). Targeted observations were obtained using the GOTO North on 2025-07-08 22:31:40 UT (8.301 minutes post-trigger). Each observation consisted of 4x90s exposures in the GOTO L-band (400-700 nm).
Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations of the same pointings. Source candidates were initially filtered using a classifier (Killestein et al. 2021) and cross-matched against a variety of contextual and minor planet catalogues. Human vetting was carried out in real time on any candidates that passed the above checks.
No new transients within the EP/WXT localisation are found, except for a variable star Gaia DR3 4587345820285675136, which is also reported by Perez-Garcia et al. GCN 41047. This source exhibited significant variability in GOTO archival L-band images, brightening from magnitude 20.2 to 18.8 (AB) between 2025-04-07 and 2025-06-15. In our post-trigger observation on 2025-07-08 at 22:31:40 UT (8.30 minutes post-trigger), the source appeared much brighter and was saturated even in our single frames, indicating it was brighter than ~12 mag.
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).
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