发表机构
Durham University; National Astronomical Observatories, Chinese Academy of Sciences（杜伦大学; 中国科学院国家天文台）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究利用DESI和eROSITA数据检验CL-AGN的盘-冕诊断，发现α_OX与爱丁顿比率的V形关系受光度估计器影响，并非独立吸积态诊断，需结合X射线光谱进一步验证。
AI 中文摘要
变化型活动星系核（CL-AGN）被认为遵循一种类似X射线双星的、在光学/紫外到X射线谱斜率 $\alpha_{\rm OX}$ 与爱丁顿比率 $\lambda_{\rm Edd}\equiv L_{\rm bol}/L_{\rm Edd}$ 之间的V形关系。我们利用从暗能量光谱仪（DESI）中选出的CL-AGN以及与eROSITA全天巡天（eRASS）匹配的控制样本检验了这一解释。我们发现，$\alpha_{\rm OX}$ 与基于光学连续谱的爱丁顿比率 $\lambda_{\rm Edd,opt}$ 之间明显的正相关性并非CL-AGN所独有，在匹配的非变化型样本中同样出现。在我们主要的统计样本——宽H$\alpha$ AGN中，这一结构很大程度上由已知的 $\alpha_{\rm OX}$ 对紫外光度的依赖以及静止系2500埃光度 $L_{2500}$、黑洞质量 $M_{\rm BH}$ 与 $\lambda_{\rm Edd,opt}$ 之间的协方差所驱动。当改用基于X射线的爱丁顿比率时，由于X射线光度 $L_X$ 以相反符号进入两个轴，该关系发生符号反转。因此，明显的 $\alpha_{\rm OX}$-爱丁顿比率V形可能由光度估计器诱导产生，并非独立的吸积态诊断。作为补充测试，我们检查了从星表波段流量推断出的eRASS有效光子指数 $\Gamma_{\rm eff}$。在宽线AGN中，它与独立于X射线的光学爱丁顿比率呈弱正相关。然而，较弱的硬波段趋势依赖于零模型，且不能孤立出冕的软化效应。这些结果促使进一步结合独立估计的爱丁顿比率进行X射线光谱分析，以检验盘-冕系统的内在变化。
英文摘要
Changing-look active galactic nuclei (CL-AGN) have been proposed to follow an X-ray-binary-like, V-shaped relation between the optical/ultraviolet-to-X-ray spectral slope, $α_{\rm OX}$, and the Eddington ratio, $λ_{\rm Edd}\equiv L_{\rm bol}/L_{\rm Edd}$. We test this interpretation using CL-AGN selected from the Dark Energy Spectroscopic Instrument (DESI) and control samples matched to the eROSITA all-sky survey (eRASS). We find that the apparent positive correlation between $α_{\rm OX}$ and the optical-continuum-based Eddington ratio, $λ_{\rm Edd,opt}$, is not unique to CL-AGN, but also appears in matched non-changing-look samples. In broad-H$α$ AGN, our main statistical sample, this structure is largely driven by the known dependence of $α_{\rm OX}$ on ultraviolet luminosity and by the covariance between the rest-frame 2500 Angstrom luminosity, $L_{2500}$, the black-hole mass, $M_{\rm BH}$, and $λ_{\rm Edd,opt}$. When an X-ray-based Eddington ratio is used instead, the relation reverses sign because the X-ray luminosity, $L_X$, enters the two axes with opposite signs. An apparent $α_{\rm OX}$-Eddington-ratio V-shape can therefore be induced by the luminosity estimator and is not a standalone accretion-state diagnostic. As a complementary test, we examine the eRASS effective photon index, $Γ_{\rm eff}$, inferred from catalogue band fluxes. In broad-line AGN, it shows a weak positive association with the X-ray-independent optical Eddington ratio. However, the weaker hard-band trend depends on the null model and does not isolate coronal softening. These results motivate further X-ray spectroscopy, combined with independently estimated Eddington ratios, to test for intrinsic changes in the disk-corona system.
Comments17 pages, 9 figures. Accepted for publication in MNRAS
