Modelling the energy dependence of black hole binary flows
Modelling the energy dependence of black hole binary flows
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DOI：
10.1093/mnras/stx2359
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发表时间：
2017-06
影响因子：
4.8
通讯作者：
Ra’ad D Mahmoud;C. Done
中科院分区：
文献类型：
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作者：
Ra’ad D Mahmoud;C. Done
假设X射线热流的光谱可以由两个康普顿化区产生，我们建立了黑洞双星低/硬态的全光谱计时模型。在流动的最大半径/最软光谱区域产生的缓慢波动向下传播，以调制在接近黑洞的光谱较硬区域产生的较快波动。观测到的光谱和变率是通过对气流中所有区域的总和产生的，包括从截断的圆盘反射的辐射。这产生了与能量相关的傅立叶滞后，与数据中的滞后性质相似。在给定粘性频率规定的情况下，该模型预测了任何能带的傅里叶功率谱密度和滞后。我们将这个模型应用于来自Cyg X-1的Rossi X射线计时探测器的存档数据，使用时间平均能谱和假设的发射率来设置软和硬康普顿化区的径向边界。我们发现，功率谱不能用任何光滑的产生波动的模型来描述，而是需要在流动中存在特定的半径，在那里噪声优先产生。我们还发现，光谱不同区域之间的涨落衰减是必要的，以防止所有在大半径产生的可变性能量传播到内部区域。即使有了这些补充，我们也可以拟合每个能量下的功率谱或能带之间的滞后，但不能同时拟合两者。我们的结论是，要么光谱比两个区域模型更复杂，要么其他过程在形成可变性中起着重要作用。
We build a full spectral-timing model for the low/hard state of black hole binaries assuming that the spectrum of the X-ray hot flow can be produced by two Comptonization zones. Slow fluctuations generated at the largest radii/softest spectral region of the flow propagate down to modulate the faster fluctuations produced in the spectrally harder region close to the black hole. The observed spectrum and variability are produced by summing over all regions in the flow, including its emission reflected from the truncated disc. This produces energy-dependent Fourier lags qualitatively similar to those in the data. Given a viscous frequency prescription, the model predicts Fourier power spectral densities and lags for any energy bands. We apply this model to archival Rossi X-ray Timing Explorer data from Cyg X-1, using the time-averaged energy spectrum together with an assumed emissivity to set the radial bounds of the soft and hard Comptonization regions. We find that the power spectra cannot be described by any smooth model of generating fluctuations, instead requiring that there are specific radii in the flow where noise is preferentially produced. We also find fluctuation damping between spectrally distinct regions is required to prevent all the variability power generated at large radii being propagated into the inner regions. Even with these additions, we can fit either the power spectra at each energy or the lags between energy bands, but not both. We conclude that either the spectra are more complex than two zone models, or that other processes are important in forming the variability.