X-ray power law spectra in active galactic nuclei
X-ray power law spectra in active galactic nuclei
复制标题
活动星系核中的 X 射线幂律光谱
DOI：
10.1051/0004-6361/200913587
复制
发表时间：
2010
影响因子：
6.5
通讯作者：
T. Courvoisier
中科院分区：
文献类型：
--
作者：
W. Ishibashi;T. Courvoisier
活动星系核的X射线谱通常被描述为幂定律谱，用光谱斜率α或光子指数Γ来表征。在这里，我们讨论了块状吸积流框架内的X射线光谱性质，并估计了作为源参数的函数的幂定律斜率。我们预计大质量天体中的光谱比质量较小的源中的光谱更硬，而高吸积率系统中的光谱则更陡峭。光子指数的预测值覆盖了塞弗特星系和类星体中典型观测到的光谱斜率范围。总体趋势与观测结果一致，这可能解释了在不同的活动星系核样品中观察到的光子指数与爱丁顿比(以及可能与黑洞质量的反相关)正相关的原因。光谱特性也与可变性特性密切相关。我们得到较短的特征时间尺度与较陡峭的谱有关。这与观测到的“光谱计时”关联是一致的。
X-ray spectra of active galactic nuclei (AGN) are usually described as power law spectra, characterized by the spectral slope α or photon index Γ. Here we discuss the X-ray spectral properties within the framework of clumpy accretion flows, and estimate the power law slope as a function of the source parameters. We expect harder spectra in massive objects than in less massive sources, and steeper spectra in higher accretion rate systems. The predicted values of the photon index cover the range of spectral slopes typically observed in Seyfert galaxies and quasars. The overall trends are consistent with observations, and may account for the positive correlation of the photon index with Eddington ratio (and the possible anticorrelation with black hole mass) observed in different AGN samples. Spectral properties are also closely related to variability properties. We obtain that shorter characteristic time scales are associated with steeper spectra. This agrees with the observed “spectral-timing” correlation.