Kavli Affiliate: Fukun Liu
| First 5 Authors: Fukun Liu, Chunyang Cao, Marek A. Abramowicz, Maciek Wielgus, Rong Cao
| Summary:
Elliptical accretion disk models for tidal disruption events (TDEs) have been
recently proposed and independently developed by two groups. Although these two
models are characterized by a similar geometry, their physical properties
differ considerably. In this paper, we further investigate the properties of
the elliptical accretion disk of the nearly uniform distribution of
eccentricity within the disk plane. Our results show that the elliptical
accretion disks have distinctive hydrodynamic structures and spectral energy
distributions, associated with TDEs. The soft X-ray photons generated at
pericenter and nearby are trapped in the disk and advected around the ellipse
because of large electron scattering opacity. They are absorbed and reprocessed
into emission lines and low-frequency continuum via recombination and
bremsstrahlung emission. Because of the rapid increase of bound-free and
free-free opacities with radius, the low-frequency continuum photons become
trapped in the disk at large radius and are advected through apocenter and back
to the photon-trapping radius. Elliptical accretion disks predict sub-Eddington
luminosities and emit mainly at the photon-trapping radius of thousands of
Schwarzschild radii with a blackbody spectrum of nearly single temperature of
typically about 3X10^4 K. Because of the self-regulation, the photon-trapping
radius expands and contracts following the rise and fall of accretion rate. The
radiation temperature is nearly independent of BH mass and accretion rate and
varies weakly with the stellar mass and the viscosity parameter. Our results
are well consistent with the observations of optical/UV TDEs.
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