Geometrical Effect of Supercritical Accretion Flows: Observational Implications of Galactic Black-Hole Candidates and Ultraluminous X-Ray Sources
Geometrical Effect of Supercritical Accretion Flows: Observational Implications of Galactic Black-Hole Candidates and Ultraluminous X-Ray Sources
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DOI：
10.1093/pasj/57.3.513
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发表时间：
2005-04
影响因子：
2.3
通讯作者：
K. Watarai;K. Ohsuga;R. Takahashi;J. Fukue
中科院分区：
文献类型：
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作者：
K. Watarai;K. Ohsuga;R. Takahashi;J. Fukue
我们考虑了在超临界吸积流中观测角度的依赖性，并讨论了星系黑洞候选者和超光x射线源的观测意义。超临界吸积流的模型谱在很大程度上依赖于倾角。例如，在低倾角下，超临界盘（吸积速率M=1000LE/C 2，黑洞质量M= IOM 8）的最高温度为kIin rv 2.0keV；S 40°，而kIin rv 0.6keV为高倾角，i 2: 60°。这种光谱软化源于盘的自掩，即外盘阻挡了盘内区域的发射，即使我们考虑到广义相对论的影响（光弯曲，多普勒增强）。这是因为，当质量吸积速率超过临界速率时，由于辐射压力的增强，圆盘的形状在几何上变厚。我们还发现，低吸积i和低吸积速率盘的光谱性质与高吸积i和高吸积速率盘的光谱性质非常相似。也就是说，如果一个天体具有高i和高吸积率，这样的系统就会遭受自掩，光谱将非常柔软。因此，我们不能仅仅通过光谱形状的不同来区分这些圆盘。相反，如果我们利用自掩星特性，我们可以约束系统的倾角。我们认为，一些观测到的高温超光x射线源具有低倾角，即近正面几何；S 40°，而银河系候选黑洞XTE 11550-564具有相对较高的倾角，为2.60°。
We consider the dependence of the viewing angle in supercritical accretion flows and discuss the observational implications of galactic black-hole candidates and ultraluminous X-ray sources. Model spectra of supercritical accretion flows strongly depend on the inclination angle. For example, the maximum temperature of the supercritical disk (the accretion rate and the black-hole mass are M=1000LE/C 2 and M =IOM 8 , respectively) is kIin rv 2.0keV for a low-inclination angle, i ;S 40°, while kIin rv 0.6keV for a high-inclination angle, i 2: 60°. This spectral softening originates from self-occultation of the disk, i.e., the outer disk blocks emission from the disk inner region, even if we take into account the effect of general relativity (light bending, Doppler boosting). This is because, when the mass accretion rate exceeds the critical rate, then the shape of the disk is geometrically thick due to enhanced radiation pressure. We also find that the spectral properties of low-i and low accretion-rate disks are very similar to those of high-i and high accretion-rate disks. That is, if an object has a high i and a high accretion rate, such a system suffers from self-occultation and the spectrum will be extremely soft. Therefore, we cannot distinguish these disks by only the difference in their spectrum shapes. Conversely, if we use the self-occultation properties, we could constrain the inclination angle of the system. We suggest that some observed high-temperature ultraluminous X-ray sources have low-inclination angles, i.e., near face-on geometry, i ;S 40°, and the Galactic black-hole candidate XTE 11550-564 possesses relatively high-inclination angles, i 2: 60°.