Kavli Affiliate: Xian Chen
| First 5 Authors: Chunyang Cao, F. K. Liu, Xian Chen, Shuo Li,
| Summary:
Quasi-periodic eruptions (QPEs) are a novel class of transients recently
discovered in a few extragalactic nuclei. It has been suggested that a QPE can
be produced by a main-sequence star undergoing repeated partial disruptions by
the tidal field of a supermassive black hole (SMBH) immediately after getting
captured on a tightly bound orbit through the Hills mechanism. In this paper,
we investigate the period-dependent formation rate of QPEs for this scenario,
utilizing scattering experiments and the loss-cone theory. We calculate the QPE
formation rates in both a single-SMBH and a dual-SMBHs system, motivated by the
over-representation of post-merger galaxies as QPE hosts. We find that for
SMBHs of mass $10^{6}-10^{7}M_{odot}$, most QPEs formed in this scenario have
periods longer than $simeq 100$ days. A single-SMBH system generally produces
QPEs at a negligible rate of $10^{-10}-10^{-8} rm{yr}^{-1}$ due to
inefficient two-body relaxation. While in a dual-SMBHs system, the QPE rate is
enhanced by $3-4$ orders of magnitude, mainly due to a boosted angular momentum
evolution under tidal perturbation from the companion SMBH (galaxy). The QPE
rate in a post-merger galactic nucleus hosting two equal-mass SMBHs separated
by a few parsecs could reach $10^{-6}-10^{-5} rm{yr}^{-1}$. Our results
suggest that a non-negligible fraction ($simeq 10-90%$) of long-period QPEs
should come from post-merger galaxies.
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