Secular Evolution of Quasiperiodic Eruptions: eRO-QPE2

Quasi-periodic eruptions (QPEs) are recurrent soft X-ray flares from galactic nuclei. In this work, we analyze both the quiescent and eruption emission of eRO-QPE2, using 11 XMM-Newton observations spanning $4.33\mathrm{y}\mathrm{r}$. The key findings include (1) the eruption peak count rate remains approximately constant, while the quiescent count rate shows an approximately linear decline superposed with a large-amplitude oscillation; (2) no secondary eruptions are detected between the normal eruptions and any such events would have to be fainter by more than two orders of magnitude; (3) the recurrence time decreases at an average rate of ${\dot{T}}_{\mathrm{r}\mathrm{e}\mathrm{c}}\approx -5\times {10}^{-6}$. These findings are consistent with an extreme mass-ratio inspiral (EMRI) interacting with a precessing accretion disk and producing two normal eruptions per orbital period. Bayesian timing analyses further constrain the EMRI orbital eccentricity to $e<0.033$ (at $95\mathrm{\%}$ confidence level).