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arXiv 0909.1069astro-ph.HEastro-ph.SR
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热吸积流内部区域整体康普顿冷却的蒙特卡罗模拟

Monte Carlo simulations of global Compton cooling in inner regions of hot accretion flows

Fu-Guo Xie, Andrzej Niedzwiecki, Andrzej A. Zdziarski, Feng Yuan

摘要:

热吸积流,如对流为主的吸积流,一般是光学薄的径向方向。因此,在某些半径产生的光子可以通过康普顿散射冷却或加热其他半径的电子。这种全球康普顿散射先前已被证明是重要的吸积流的动力学。在这里,我们使用精确的全球广义相对论蒙特卡罗模拟扩展这个问题的以前的治疗。我们研究了吸积流的内部区域(R < 600R_g),得到了整体自洽解。与初始的非自洽解相比,最终解在大于等于10个引力半径处的冷却速率和电子温度都显著降低。另一方面,自洽解的辐射谱具有与初始迭代的辐射谱相似的形状,除了高能量截止在低约2倍的能量处,并且测辐射光度降低约2倍。我们还比较了全球康普顿散射模型与局部模型在球形和平板几何。我们发现,平板模型近似的全球模型显着优于球形。尽管如此,两个局部模型都不能很好地近似冷却速率的径向分布,并且差异可以高达两个数量级。局部平板模型低估了外部区域的冷却速率,而高估了内部区域的冷却速率。我们比较我们的建模结果观察到的硬态光谱的黑洞双星,并找到一个整体良好的协议提供任何磁盘流出是弱的。我们发现,广义相对论效应的流动动力学修改全球康普顿化是至关重要的,在接近这一协议。

英文摘要:

Hot accretion flows such as advection-dominated accretion flows are generally optically thin in the radial direction. Thus photons generated at some radii can cool or heat electrons at other radii via Compton scattering. Such global Compton scattering has previously been shown to be important for the dynamics of accretion flows. Here, we extend previous treatments of this problem by using accurate global general relativistic Monte Carlo simulations. We focus on an inner region of the accretion flow (R < 600R_g), for which we obtain a global self-consistent solution. As compared to the initial, not self-consistent solution, the final solution has both the cooling rate and the electron temperature significantly reduced at radii >=10 gravitational radii. On the other hand, the radiation spectrum of the self-consistent solution has the shape similar to that of the initial iteration, except for the high-energy cut-off being at an energy lower by a factor of ~2 and the bolometric luminosity decreased by a factor of ~2. We also compare the global Compton scattering model with local models in spherical and slab geometry. We find that the slab model approximates the global model significantly better than the spherical one. Still, neither local model gives a good approximation to the radial profile of the cooling rate, and the differences can be up to two orders of magnitude. The local slab model underestimates the cooling rate at outer regions whereas it overestimates that rate at inner regions. We compare our modelling results to observed hard-state spectra of black-hole binaries and find an overall good agreement provided any disc outflow is weak. We find that general-relativistic effects in flows which dynamics is modified by global Comptonization is crucial in approaching this agreement.

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