arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 2012.05552astro-ph.HEgr-qc
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作为潮汐扰动事件模型的椭圆形吸积盘

Elliptical accretion disk as a model for tidal disruption events

Fukun Liu, Chunyang Cao, Marek A. Abramowicz, Maciek Wielgus, Rong Cao, Zhiqin Zhou

摘要:

最近,两个研究小组提出并独立发展了潮汐扰动事件(TDE)的椭圆形吸积盘模型。虽然这两种模型的特征在于相似的几何形状,但它们的物理性质有很大的不同。本文进一步研究了椭圆形吸积盘在盘平面内偏心率近似均匀分布的性质。结果表明,椭圆形吸积盘具有独特的流体动力学结构和光谱能量分布,并伴随着TDEs。在近心及其附近产生的软X射线光子被捕获在圆盘中,并由于大的电子散射不透明度而围绕椭圆平流。它们被吸收并通过复合和韧致辐射重新加工成发射线和低频连续谱。由于束缚-自由和自由-自由不透明度随半径的迅速增加,低频连续谱光子在大半径处被捕获,并通过远心平流回到光子捕获半径。椭圆形吸积盘的亮度低于爱丁顿,主要在几千个史瓦西半径的光子俘获半径处发射,黑体光谱几乎是单一温度,典型的温度约为3 × 10^4 K。由于自调节作用,光子俘获半径随吸积率的升降而伸缩。辐射温度几乎与黑洞质量和吸积率无关,随恒星质量和粘性参数的变化很小。我们的结果与光学/紫外TDEs的观测结果是一致的。

英文摘要:

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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