AI 中文总结
研究通过长期多波段光曲线在已知 CL-AGN 样本中搜索 RCL AGNs，确认 25 个包括 22 个新发现的，分析其性质，发现转变间隔、爱丁顿比率等特征，支持吸积流驱动电离发射变化，BLR 呼吸产生 RCL 转变的观点。
AI 中文摘要
变化外观的活动星系核（CL AGNs）在数年时间尺度上显示出宽发射线的出现或消失。其中，重复 CL（RCL）AGNs 可能为理解 CL 转变提供清晰线索。我们利用长期多波段光曲线在已知 CL-AGN 样本中搜索 RCL AGNs，选出 34 个候选者进行光谱后续观测。确认了 25 个 RCL AGNs，包括 22 个新发现的。分析了这些 RCL AGNs 的性质，第二次转变的观测静止帧间隔大多为 3 - 4 年，光学光曲线变化表明有些转变可能在数月时间尺度发生。最新光谱显示开/关状态对应更高/更低爱丁顿比率。7 个 RCL AGNs 被近连续单波段光曲线良好覆盖，其开/关状态遵循多年光学变化，爱丁顿比率随光度变化一致。还发现仅 Hβ 转变发生时的爱丁顿比率高于涉及 Hα 和 Hβ 的转变，表明宽线区（BLR）可见性阈值与谱线有关。这些结果支持不同吸积流过程驱动中心电离发射可逆变化，而观测到的 RCL 转变由 BLR 跨越与谱线有关的可见性阈值呼吸产生的图景。
英文摘要
Changing-look active galactic nuclei (CL AGNs) show the appearance or disappearance of broad emission lines on timescales of years. Among them, the repeating CL (RCL) AGNs may provide a clear clue for our understanding of the CL transitions because the same nucleus crosses some physical boundaries more than once. We search for RCL AGNs in known CL-AGN samples using long-term multi-band light curves, and selected 34 candidates for spectroscopic follow-up. We confirm 25 RCL AGNs, including 22 newly identified cases. Properties of these RCL AGNs are analyzed. The observed rest-frame intervals of the second transitions are mostly 3--4 yr, while the variations of the optical light curves suggest that some transitions might occur on timescales of several months. The latest spectra show that the on/off states correspond to higher/lower Eddington-ratio, in the expected direction relative to the parent CL-AGN samples. As seven RCL AGNs are well covered by nearly continuous single-band light curves, their on/off states can be found to follow multi-year optical excursions, and their Eddington ratios vary consistently with the photometric changes. We also find that the H$β$-only transitions occur at higher Eddington ratios than the transitions involving both H$α$ and H$β$, suggesting a line-dependent Broad-Line-Region (BLR) visibility threshold. These results support a picture in which different accretion-flow processes drive reversible changes in the central ionizing emissions, while the observed RCL transitions are produced by the BLR breathing across line-dependent visibility thresholds.
Comments22 pages, 11 figures, 2 tables, submitted to ApJ
