Quasi-periodic eruptions as a probe of accretion disc in tidal disruption events

ABSTRACT Quasi-periodic eruptions (QPEs) are X-ray transients characterized by nearly regular recurring flares from galactic nuclei. Recent observations have confirmed that some QPEs occur in galactic centres that experienced a tidal disruption event (TDE) a few years earlier. This may be reasonably explained if QPEs are produced when a star orbiting a supermassive black hole passes through an accretion disc formed by the TDE. Based on this scenario, we investigate the expected QPE signatures in the early stages of TDEs, taking into account the time evolution of the accretion disc. In the early phase, the disc is in a super-Eddington accretion state. The interaction between the star and such a slim disc results in QPEs with durations of $\sim 100\!-\!1000\, {\rm s}$ and temperatures of $\sim 1{\!-\!}100\, {\rm keV}$, which are significantly shorter and hotter than those of the currently detected QPE population. These events are detectable with current X-ray telescopes, but their small duty cycle ($\lesssim 1~{{\ \rm per\ cent}}$) and the potential presence of a massive disc wind may make detection challenging. We encourage early-time and long-term monitoring TDEs showing X-rays to capture these QPEs, as such detections would provide valuable insights into the disc formation process in TDEs.