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arXiv · 2510.26682

An extremely fast fading population II dwarf nova candidate: caught spectroscopically on the rise

Natasha Van Bemmel·Jielai Zhang·Jeff Cooke·Anais Möller·Igor Andreoni·Katie Auchettl·David Buckley·Jonathan Carney·Dougal Dobie·James Freeburn·Bruce Gendre·Vanshika Kansal·Itumeleng Monageng·Arne Rau·Nikita Rawat·Mark Suhr·Edward N. Taylor
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Abstract

We present AT2022kak, a rapidly evolving optical transient discovered by the KiloNova and Transients Program (KNTraP). This interesting burst exhibited extremely fast evolution, with a large amplitude blue outburst of m > 3.3 in a single night, and a rapid fade back to quiescence in the following two nights. We deployed a multi-wavelength follow-up campaign, monitoring the object for the next two months, but saw no recurrent burst. Three years later, while observing to get spectroscopy of the object in quiescence, there was a new outburst, enabling the collection of time-resolved spectra of the rise and fade of the outburst. The light curve properties of the first burst and spectra of the second burst are consistent with a dwarf nova. Its fast evolving behaviour makes it one of the fastest and faintest dwarf novae observed. The estimated distance of AT2022kak from the Galactic centre is ~6.6 kpc, with a scale height of ~2 kpc. This scale height places it in the Galactic thick disk, where only very few dwarf novae have been found, and is therefore a potential Population II dwarf novae system.

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Natasha Van Bemmel, Jielai Zhang, Jeff Cooke, Anais Möller, Igor Andreoni, Katie Auchettl, David Buckley, Jonathan Carney, Dougal Dobie, James Freeburn, Bruce Gendre, Vanshika Kansal, Itumeleng Monageng, Arne Rau, Nikita Rawat, Mark Suhr, Edward N. Taylor. 2025-10-30. An extremely fast fading population II dwarf nova candidate: caught spectroscopically on the rise. https://doi.org/10.1093/mnras%2Fstag309

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