The Emergent Population of Repeating Nuclear Transients

Galactic nuclei showing recurrent phases of activity and quiescence have recently been discovered, with recurrence times as short as a few hours to a day — known as quasi-periodic X-ray eruption (QPE) sources — to as long as hundreds to a thousand days for repeating nuclear transients (RNTs), several of those originating from previously quiescent nuclei. This talk will first summarize the current sample of repeating nuclear transients and their main multi-wavelength properties. I will also present our recent discovery of Swift J0230+28, a source that exhibits soft X-ray quasi-periodic eruptions from the nucleus of a previously unremarkable galaxy at ~ 165 Mpc, with a recurrence time of approximately 22 days, an intermediary timescale between known RNTs and QPE sources - which may the missing connection between these two populations. Finally, I will discuss our current understanding of these transients as a population, as likely electromagnetic counterparts of extreme mass ratio inspirals (EMRIs) and probes for nuclear stellar dynamics in external galaxies.