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arXiv 1306.2475astro-ph.HE
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天鹅座X-1中非常快的X射线光谱变化:硬态和软态发射成分的起源

Very fast X-ray spectral variability in Cygnus X-1: Origin of the hard and soft-state emission components

Chris J. Skipper, Ian M. McHardy, Thomas J. Maccarone

摘要:

X射线光子指数Γ作为计数率的函数变化的方式是对吸积致密物体周围的发射过程和发射几何的强诊断。在这里,我们提出了一项研究的结果,使用一种新的,简单的方法,旨在提高灵敏度的测量非常短的时间尺度上的变化。我们测量了高质量X射线双星天鹅座X-1的~ 200万个光谱中的Γ,这些光谱是从具有各种不同吸积速率和光谱状态的观测中提取的,时间尺度短至16 ms,并将这些测量与源计数率进行了交叉相关。在软态交叉关联函数(CCF)中,我们发现在零滞后处有一个正的峰值,在较软的观测值中更强更窄。假设X射线是由日冕中高能电子对软种子光子的康普顿散射产生的,这些结果与来自吸积盘内边缘的种子光子对日冕的康普顿冷却是一致的,吸积盘的截断半径随着硬度的增加而增加。比率。然而,从硬态观测产生的CCF显示出反相关性,这是最容易解释的电晕中的电子的能量的变化,而不是在种子光子通量的变化。硬态的CCF可以被分解成一个狭窄的反相关零滞后,我们暂时关联的自康普顿化的循环同步加速器种子光子的影响,无论是热的,光学薄吸积流或基地的喷气,和第二个,不对称的组件,我们建议产生的结果之间的滞后的软和硬X射线发射。滞后可能是由Comptonising电子中的径向温度/能量梯度与吸积率扰动的向内传播相结合引起的。

英文摘要:

The way in which the X-ray photon index, Γ, varies as a function of count rate is a strong diagnostic of the emission processes and emission geometry around accreting compact objects. Here we present the results from a study using a new, and simple, method designed to improve sensitivity to the measurement of the variability of Γ on very short time-scales. We have measured Γ in ~2 million spectra, extracted from observations with a variety of different accretion rates and spectral states, on time-scales as short as 16 ms for the high mass X-ray binary Cygnus X-1, and have cross-correlated these measurements with the source count rate. In the soft-state cross-correlation functions (CCFs) we find a positive peak at zero lag, stronger and narrower in the softer observations. Assuming that the X-rays are produced by Compton scattering of soft seed photons by high energy electrons in a corona, these results are consistent with Compton cooling of the corona by seed photons from the inner edge of the accretion disc, the truncation radius of which increases with increasing hardness ratio. The CCFs produced from the hard-state observations, however, show an anti-correlation which is most easily explained by variation in the energy of the electrons in the corona rather than in variation of the seed photon flux. The hard-state CCFs can be decomposed into a narrow anti-correlation at zero lag, which we tentatively associate with the effects of self-Comptonisation of cyclo-synchrotron seed photons in either a hot, optically thin accretion flow or the base of the jet, and a second, asymmetric component which we suggest is produced as a consequence of a lag between the soft and hard X-ray emission. The lag may be caused by a radial temperature/energy gradient in the Comptonising electrons combined with the inward propagation of accretion rate perturbations.

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