Extracting information from AGN variability
Extracting information from AGN variability
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从 AGN 变化中提取信息
DOI：
10.1093/mnras/stx1420
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发表时间：
2016
影响因子：
4.8
通讯作者：
G. Richards
中科院分区：
文献类型：
--
作者：
V. Kasliwal;M. Vogeley;G. Richards
活动星系核在整个电磁频谱上表现出快速、高振幅的随机通量变化，时间尺度从数小时到数年不等。这种变化的原因知之甚少。我们提出了一种新的方法，使用可变性（1）测量的时间尺度上的通量扰动演变和（2）特征的驱动通量扰动。我们将活动星系核的观测光变曲线模型化为一个由随机脉冲驱动的线性微分方程。从物理上讲，这些脉冲可能是吸积盘中的局部“热点”---线性微分方程控制着热点如何演变和消散。吸积盘材料的脉冲响应函数由线性微分方程的绿色函数给出。热点辐射能量的时间尺度由驱动随机脉冲的功率谱表征。我们分析了Kepler AGN Zw 229-15的光变曲线，发现观测到的光变行为可以用一个受色噪声扰动的阻尼谐振子模型来描述。模型功率谱在385 ~d时间尺度上翻转。在较短的时间尺度上，对数功率谱斜率在2美元和4美元之间变化，解释了以前研究中注意到的行为。我们恢复和识别的$5.6$~d和$67$~d的时间尺度报告以前的工作。这些时间尺度分别表示通量扰动增长的时间尺度和通量扰动衰减回稳态通量水平的时间尺度。我们将使用我们的方法研究光变曲线的软件包\textsc{k\={a}l\={i}}提供给社区。
AGN exhibit rapid, high amplitude stochastic flux variability across the entire electromagnetic spectrum on timescales ranging from hours to years. The cause of this variability is poorly understood. We present a new method for using variability to (1) measure the time-scales on which flux perturbations evolve and (2) characterize the driving flux perturbations. We model the observed light curve of an AGN as a linear differential equation driven by stochastic impulses. Physically, the impulses could be local `hot-spots' in the accretion disk---the linear differential equation then governs how the hot spots evolve and dissipate. The impulse-response function of the accretion disk material is given by the Green's function of the linear differential equation. The timescales on which the hot-spots radiate energy is characterized by the powerspectrum of the driving stochastic impulses. We analyze the light curve of the \Kepler AGN Zw 229-15 and find that the observed variability behavior can be modeled as a damped harmonic oscillator perturbed by a colored noise process. The model powerspectrum turns over on time-scale $385$~d. On shorter time-scales, the log-powerspectrum slope varies between $2$ and $4$, explaining the behavior noted by previous studies. We recover and identify both the $5.6$~d and $67$~d timescales reported by previous work. These timescales represent the time-scale on which flux perturbations grow, and the time-scale on which flux perturbations decay back to the steady-state flux level respectively. We make the software package used to study light curves using our method, \textsc{k\={a}l\={i}}, available to the community.
DOI：
10.1111/j.1365-2966.2006.10871.x
发表时间：
2006-07
影响因子：
4.8
作者：
P. Arévalo;I. Papadakis;P. Uttley;I. McHardy;W. Brinkmann
通讯作者：
P. Arévalo;I. Papadakis;P. Uttley;I. McHardy;W. Brinkmann