发表机构
Yunnan University（云南大学）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
研究1ES 1927+654在2018 - 2024年演化期间X射线随机变异性，利用XMM - Newton数据和高斯过程建模，发现恢复阶段有变异性转变，还呈现不同阶段特征，为AGN日冕随机变异性变化提供探测手段。
AI 中文摘要
我们研究了可变型活跃星系核1ES 1927+654在2018 - 2024年演化期间的随机X射线变异性，重点关注其2018年坍缩后X射线日冕的恢复。利用XMM - Newton EPIC - pn在0.3 - 2.0 keV和2.0 - 10.0 keV波段的光变曲线，用高斯过程（GP）协方差分量建模变异性。贝叶斯模型比较揭示了恢复阶段的X射线随机变异性转变。在2019年5月5日观测中，单次连续曝光内协方差从类似Matérn - 3/2状态变为类似DRW状态。现象学门控核估计将此转变定位在硬波段特定时刻。这一转变发生在日冕重新出现后但在其明显硬化和变亮之前，表明盘 - 日冕重新配置的早期时域特征。后期观测中，与已知毫赫兹QPO相关的类似SHO分量特征频率和品质因数增加。基于GP的时域推断为恢复中的AGN日冕随机变异性变化提供了灵敏探测。
英文摘要
We investigate the stochastic X-ray variability of the changing-look active galactic nucleus 1ES 1927+654 during its 2018--2024 evolution, focusing on the recovery of the X-ray corona after its 2018 collapse. Using XMM-Newton EPIC-pn light curves in the 0.3--2.0 keV and 2.0--10.0 keV bands, we model the variability with Gaussian process (GP) covariance components including Matérn-3/2, damped-random-walk (DRW), stochastically driven damped simple-harmonic-oscillator (SHO), and white-noise terms. Bayesian model comparison reveals an X-ray stochastic-variability transition during the changing-look recovery phase. In the 2019 May 5 observation, the preferred covariance changes from a Matérn-3/2-like state to a DRW-like state within a single continuous exposure. A phenomenological gated-kernel estimate localizes this transition sharply in the hard band at $t_c\simeq23.5~{\rm ks}$, while the soft band shows the same qualitative change over a broader interval. This transition occurs after the X-ray corona had reappeared but before the later pronounced hardening and brightening of the coronal emission, suggesting an early timing-domain signature of disk--corona reconfiguration. Phenomenologically, the dominant variability evolves from a smoother, finite-memory correlated process to a rougher, shorter-memory red-noise process. In the later 2022--2024 observations, SHO-like components associated with the known millihertz QPO show increasing characteristic frequency and quality factor, indicating a faster and more coherent oscillatory component during the QPO-plus-jet phase. GP-based time-domain inference therefore provides a sensitive probe of stochastic-variability changes in recovering AGN coronae.
Comments12 pages, 4 figures. Accepted for publication in The Astrophysical Journal
