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arXiv 1003.1430astro-ph.HE
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黑洞X射线双星盘状日冕和内部热流的辐射谱

Radiative Spectra from Disk Corona and Inner Hot Flow in Black Hole X-ray Binaries

Ryoji Kawabata, Shin Mineshige

摘要:

为了理解黑洞X射线双星在低/硬态时硬X射线辐射的起源,我们计算了以下三种热介质和冷介质配置下黑洞吸积流的X射线谱:(a)内部热流和外部冷盘(b)冷盘夹在盘冠之间(盘冠模型),以及(c)这两种模型的组合(混合模型)。我们要求成功的模型的基本特征是(i)显著的硬X射线发射,其亮度超过软X射线,(ii)高的硬X射线亮度在(0.4 - 30)× 10^{37} erg s^{-1};(iii)在硬X射线带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)和较硬(>10 keV)幂律分量的光子指数。不考虑非热电子的贡献,也不考虑随时间变化的演化。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)才能解释足够强的硬X射线发射,以及两个幂律分量的存在,因为日冕中的吸积率与薄盘中的吸积率之比很大。外盘日冕(其中康普顿y参数较小,y < 1)产生光子指数为Gamma_s ~ 2的较软幂律分量,而内热流(其中y gtrsim 1)产生Gamma_h < 2的较硬分量。该模型还可以解释所观察到的光子指数和反射分数之间的关系。

英文摘要:

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) and the harder (>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.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

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