Spectral energy distribution of super-Eddington flows
Spectral energy distribution of super-Eddington flows
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DOI：
10.1111/j.1365-2966.2006.10926.x
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发表时间：
2006-08
影响因子：
4.8
通讯作者：
D. Heinzeller;S. Mineshige;K. W. I. F. Astrophysik;U. Heidelberg;G. M. F. N. Physics;Kyoto University;J. D. O. Physics;R. University;Tokyo;Japan.
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文献类型：
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作者：
D. Heinzeller;S. Mineshige;K. W. I. F. Astrophysik;U. Heidelberg;G. M. F. N. Physics;Kyoto University;J. D. O. Physics;R. University;Tokyo;Japan.
用平行视线计算方法研究了超Eddington吸积流的谱特性。次表层模型取自Ohsuga等人的二维辐射流体动力学模拟。(2005)，由一个盘吸积区和一个具有高速外流的延伸大气组成。采用通量限制扩散近似，求解了考虑相对论效应的非灰色辐射传递方程。计算出的光谱由来自圆盘的类似黑体的热辐射以及来自大气的高能X射线和伽马射线发射组成，该辐射与倾角有关。我们发现在小倾角的热辐射中有轻微的束流效应。如果我们比较正面情况和边缘情况，主要是由于多普勒增强，平均光子能量增加了∼1.7倍，而光子数密度增加了∼3.7倍，这主要是由于中心黑洞周围各向异性物质的分布。这解释了观测到的超低能X射线的X射线温度，这些温度太高，无法在中等质量黑洞的框架内解释。虽然热谱成分的主要特征与对薄吸积盘的更详细计算相一致，但大气在高能部分引起了重大变化，这是现有模型无法再现的。我们还得出结论，为了正确解释观测数据，不能采用像埃丁顿-巴比尔近似这样的简单方法。
Spectral properties of super-Eddington accretion flows are investigated by means of a parallel line-of-sight calculation. The subjacent model, taken from the two-dimensional radiation hydrodynamic simulations by Ohsuga et al. (2005), consists of a disc accretion region and an extended atmosphere with high-velocity outflows. The non-grey radiative transfer equation is solved, including relativistic effects, by applying the flux-limited diffusion approximation. The calculated spectrum is composed of a thermal, blackbody-like emission from the disc which depends sensitively on the inclination angle, and of high-energy X-ray and gamma-ray emission from the atmosphere. We find mild beaming effects in the thermal radiation for small inclination angles. If we compare the face-on case with the edge-on case, the average photon energy is larger by a factor of ∼1.7 due mainly to Doppler boosting, while the photon number density is larger by a factor of ∼3.7 due mainly to anisotropic matter distribution around the central black hole. This gives an explanation for the observed X-ray temperatures of ULXs which are too high to be explained in the framework of intermediate-mass black holes. While the main features of the thermal spectral component are consistent with more detailed calculations of slim accretion discs, the atmosphere induces major changes in the high-energy part, which cannot be reproduced by existing models. We also conclude that, in order to interpret the observational data properly, simple approaches like the Eddington–Barbier approximation cannot be applied.