GOTO065054.49+593624.51: Discovery of a bright optical galactic transient

ATel #16842; T. Killestein (University of Turku), L. Kelsey, G. Ramsay, M. R. Kennedy, A. Kumar, E. Wickens, K. Ackley, M. J. Dyer, J. Lyman, K. Ulaczyk, F. Jimenez-Ibarra, D. Steeghs, D. K. Galloway, V. Dhillon, P. O'Brien, K. Noysena, R. Kotak, R. P. Breton, L. K. Nuttall, E. Palle, D. Pollacco, D O’Neill, and citizen scientists: Rosemary Billington, Virgilio Gonano, Svetoslav Alexandrov, Antonio Pasqua, Cledison Marcos da Silva, report on behalf of the GOTO collaboration
on 4 Oct 2024; 12:29 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Mark Kennedy (kennedy.mark@manchester.ac.uk)

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We report the discovery of a bright optical transient, GOTO065054.49+593624.51.

During the routine all-sky survey of the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024), we detected a new, extremely bright transient source in images (4x45s) taken Oct. 4 2024 03:36:36 UT. The source, previously uncatalogued, is detected at J2000 coordinates RA = 06:50:54.49, Dec = +59:36:24.51, with a magnitude in the GOTO L-band (400-700 nm; approximately g + r) of L = 13.37 +/- 0.01. Images were immediately processed with the GOTO pipeline, and differenced using deeper template observations. GOTO all-sky survey observations from 2 nights prior (Oct. 2 2024 03:36:32 UT) show no evidence for this source down to a 5-sigma limiting magnitude of L ~ 20.2. Magnitudes were calibrated using ATLAS-REFCAT2 (Tonry et al. 2018) and are not corrected for Galactic extinction, approx E(B-V) of 0.07.

We note that this source was identified first by citizen scientist volunteers as part of the Kilonova Seekers citizen science project (Killestein and Kelsey et al. 2024) on the Zooniverse, just 3 hours after the initial discovery image was taken.

We identify a faint, blue point source underlying in deep Legacy Survey (Dey et al. 2019) imaging, with magnitudes g = 21.84, r = 21.68, z = 22.02, implying an outburst of around 8.5 mag in amplitude. The blue nature of the underlying source suggests this may be a nova outburst from a CV, but further observations are needed to confirm. Photometry retrieved via the ATLAS Forced Photometry server (Shingles et al. 2021) shows no prior outbursts of this source over a span of multiple years. The detection has been cross-checked against minor planets and other contextual catalogues.

Follow-up observations are strongly encouraged, especially spectroscopy, to ascertain the nature of this bright galactic transient.

GOTO 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).

Kilonova Seekers citizen science project