论文标题
通过模拟估算AGN的长期功率频谱密度
Estimating longterm power spectral densities in AGN from simulations
论文作者
论文摘要
功率谱密度（PSD）代表量化活性银河核（AGN）等可变源中随机或随机噪声类型波动的关键特性。近年来，PSD的估计已通过改进，观察到的光曲线的质量以及对模拟进行建模的估计。这有助于量化可变性，包括评估准周期振荡的重要性。进行此类估计的一个核心假设是非平稳性较弱。这是针对幂律PSD指数的来源，而不是一个积分功率散开的。结果，对通量概率密度函数（PDF）和PSD的估计值相互链接。通常，为了评估来自Lightcurves的两个属性的参数，无法避免使用复杂且计算昂贵的多维，多参数模型，并且更难约束和解释。但是，如果我们只希望像通常这样计算PSD索引，我们可以使用更简单的模型。我们探索弯曲的幂律模型，而不是简单的幂律作为时间序列模拟的输入，以测试重建质量。检查古典Blazar MRK 421的长期可变性，延伸到多年来，这是Fermi-lat或Swift-Bat Lightcurves的典型变化，我们发现，在特征性的时间表上，从粉红色（PSD索引一号）到白噪声的过渡，$ t_b \ sim 500-1000 $，与viscous the dis the disscale for dis usk dis usk diss confuscation comporty for dis usce for dis usception compluct cormustation。这既是一个出于身体的动机，也是一个可用于计算PSD指数的计算高效模型。
The power spectral density (PSD) represents a key property quantifying the stochastic or random noise type fluctuations in variable sources like Active Galactic Nuclei (AGN). In recent years, estimates of the PSD have been refined by improvements in both, the quality of observed lightcurves and modeling them with simulations. This has aided in quantifying the variability including evaluating the significance of quasi-periodic oscillations. A central assumption in making such estimates is that of weak non-stationarity. This is violated for sources with a power-law PSD index steeper than one as the integral power diverges. As a consequence, estimates of the flux probability density function (PDF) and PSD are interlinked. In general, for evaluating parameters of both properties from lightcurves, one cannot avoid a multi-dimensional, multi-parameter model which is complex and computationally expensive, as well as harder to constrain and interpret. However, if we only wish to compute the PSD index as is often the case, we can use a simpler model. We explore a bending power-law model instead of a simple power-law as input to time-series simulations to test the quality of reconstruction. Examining the longterm variability of the classical blazar Mrk 421, extending to multiple years as is typical of Fermi-LAT or Swift-BAT lightcurves, we find that a transition from pink (PSD index one) to white noise at a characteristic timescale, $t_b \sim 500-1000$ years, comparable to the viscous timescale at the disk truncation radius, seems to provide a good model for simulations. This is both a physically motivated as well as a computationally efficient model that can be used to compute the PSD index.
