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Collisions with tidal disruption event discs: implications for quasi-periodic X-ray eruptions

Year: 2025
Type: article
Abstract: ABSTRACT A popular class of models for interpreting quasi-periodic X-ray eruptions (QPEs) from galactic nuclei invoke collisions between an object on an extreme mass ratio inspiral (EMRI) and an accretion disc around a supermassive black hole. There are strong links between QPE systems and those discs which formed following a tidal disruption event (TDE), and at least two events (AT2019qiz and AT2022upj) are known to have occurred following an otherwise typical TDE. We show that the fact that these discs were formed following a TDE strongly constrains their properties, more so than previous models have assumed. Models based on steady-state active galactic nucleus–like discs have mass contents which grow strongly with size $M_{\rm disk}\propto R_{\rm out}^{7/2}$ and do not conserve the mass or angular momentum of the disrupted star. A very different scaling must be satisfied by a TDE disc in order to conserve the disrupted stars angular momentum, $M_{\rm disk} \propto R_{\rm out}^{-1/2}$. These constraints substantially change the predicted scaling relationships between QPE observables (luminosity, duration, energy, temperature) and the QPE period. They also allow QPE observables to be written in terms of the properties of the two stars assumed to be involved (the one tidally disrupted and the one on an EMRI), making plausibility tests of these models possible. We show that these modifications to the disc structure imply that (i) QPEs cannot be powered by collisions between an orbiting black hole and a TDE disc, (ii) QPEs also cannot be powered by collisions between the surface of a stellar EMRI and a TDE disc. A framework in which the collisions are between a TDE disc and a star which has puffed up to fill its Hill sphere with a trailing debris stream (as seen in recent simulations) cannot be ruled out from the data, and should be the focus of further study.
DOI: 10.1093/mnras/staf1658
Language: English
Open Access status: gold
Estimated APC paid: $3,046
OpenAlex ID: W4414570705
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