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

Abstract

In the first observational run of the Kilonova and Transients Programme (KNTraP), a rapidly evolving optical transient, KNTraP2022-02a (TNS name: AT2022kak), was discovered. 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 multiwavelength follow-up campaign, monitoring the object for the next two months, but saw no recurrent burst. Three years later, while obtaining 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 prop..