Radiative Spectra from Disk Corona and Inner Hot Flow in Black-Hole X-Ray Binaries
Radiative Spectra from Disk Corona and Inner Hot Flow in Black-Hole X-Ray Binaries
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DOI：
10.1093/pasj/62.3.621
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发表时间：
2010-03
影响因子：
2.3
通讯作者：
R. Kawabata;S. Mineshige
中科院分区：
文献类型：
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作者：
R. Kawabata;S. Mineshige
为了了解黑洞X射线双星在低/硬状态期间发射硬X射线的起源，我们计算了以下三种热介质和冷介质配置的黑洞吸积流的X射线光谱：（a）内部热流和冷外盘（内热流模型），（b）夹在盘冕（盘日冕模型）中的冷盘，以及（c）这两者的组合（混合模型）。我们对成功模型所需的基本特征是（i）显着的硬X射线发射，其光度超过软X射线，（ii）高硬X射线光度在（0.4 - 30）倍10^{37} erg s^{-1}范围内，以及（iii）硬X射线波段中存在两个幂律分量，其光子指数为Gamma_s ~ 2 > Gamma_h，其中Gamma_s 和 Gamma_h 分别是较软（10 keV）幂律分量的光子指数。不考虑非热电子的贡献或随时间演化的贡献。我们发现模型（a）和（b）可以被排除，因为光谱总是由软分量主导，并且最多只能再现一个幂律分量。只有模型 (c) 可以解释足够强的硬 X 射线发射，以及两个幂律分量的存在，以实现日冕中吸积率与薄盘中吸积率的较大比率。外盘日冕（康普顿 y 参数较小，y < 1）产生较软的幂律分量，光子指数为 Gamma_s ~ 2，而内部热流（其中 y gtrsim 1）产生较硬的分量，Gamma_h < 2。该模型还可以解释观察到的光子指数与反射分数之间的关系。
To understand the origin of hard X-ray emissions from black hole X-ray binaries during their low/hard states, we calculate the X-ray spectra of black-hole accretion flow for the following three configurations of hot and cool media: (a) an inner hot flow and a cool outer disk (inner hot flow model), (b) a cool disk sandwiched by disk coronae (disk corona model), and (c) the combination of those two (hybrid model). The basic features we require for successful models are (i) significant hard X-ray emission whose luminosity exceeds that of soft X-rays, (ii) high hard X-ray luminosities in the range of (0.4 - 30) times 10^{37} erg s^{-1}, and (iii) the existence of two power-law components in the hard X-ray band with the photon indices of Gamma_s ~ 2 > Gamma_h, where Gamma_s and Gamma_h are the photon indices of the softer ( 10 keV) power-law components, respectively. Contribution by non-thermal electrons nor time-dependent evolution are not considered. We find that Models (a) and (b) can be ruled out, since the spectra are always dominated by the soft component, and since only one power-law component, at most, can be reproduced. Only Model (c) can account for sufficiently strong hard X-ray emissions, as well as the existence of the two power-law components, for a large ratio of the accretion rate in the corona to that in the thin disk. The outer disk corona (where the Compton y-parameter is smaller, y < 1) produces the softer power-law component with photon index of Gamma_s ~ 2, whereas the inner hot flow (where y gtrsim 1) generates the harder component with Gamma_h < 2. This model can also account for the observed relationship between the photon index and the reflection fraction.