论文标题
用随机过程方法表征活性银河核的$γ$ ray变异性
Characterizing the $γ$-Ray Variability of Active Galactic Nuclei with Stochastic Process Method
论文作者
论文摘要
$γ$ - 时代域的天文学已经进一步进一步发展，因为已经报道了很多不同时间尺度上活性银河核（AGN）的变化。我们通过将随机工艺方法应用于Fermi-Large Area talescope（Fermi-LAT）获得的〜12.7年长期光曲线（LC），研究了23个喷射AGN的$γ$射线变异性。在这种方法中，随机驱动的阻尼简单谐波振荡器（SHO）和阻尼随机步行（DRW）模型用于对长期LCS进行建模。我们的结果表明，SHO和DRW模型都可以很好地表征23个AGN的长期变化。但是，SHO模型在过度抑制模式下受到限制，并且参数受到限制。 SHO功率频谱密度（PSD）与典型的DRW PSD相同。在对应于PSD与黑洞质量中的频率的剩余时间尺度的情节中，固有的$γ$ ray-ray特性时间尺度占据了几乎相同的空间，而光学可变性时间尺度是从积聚盘发射中获得的。这表明喷气机和积聚盘之间有联系。与AGN积聚磁盘的光学变异性相同，$γ$ ray的时间表也与AGN标准积聚磁盘中的热不稳定性引起的热时间尺度一致。
The $γ$-ray astronomy in time domain has been by now progressed further as the variabilities of Active Galactic Nuclei (AGNs) on different timescales have been reported a lot. We study the $γ$-ray variabilities of 23 jetted AGNs through applying a stochastic process method to the ~12.7 yr long-term light curve (LC) obtained by Fermi-Large Area Telescope (Fermi-LAT). In this method, the stochastically driven damped simple harmonic oscillator (SHO) and the damped random walk (DRW) models are used to model the long-term LCs. Our results show that the long-term variabilities of 23 AGNs can be characterized well by both SHO and DRW models. However, the SHO model is restricted in the over-damped mode and the parameters are poorly constrained. The SHO power spectral densities (PSDs) are same as the typical DRW PSD. In the plot of the rest-frame timescale that corresponds to the broken frequency in the PSD versus black hole mass, the intrinsic $γ$-ray characteristic timescales of 23 AGNs occupy almost the same space with the optical variability timescales obtained from the accretion disk emission. This suggests a connection between the jet and the accretion disk. Same as the optical variability of AGN accretion disk, the $γ$-ray timescale is also consistent with the thermal timescale caused by the thermal instability in the standard accretion disk of AGN.
