We present an analysis of historical multiwavelength emission of the `Changing Look' (CL) Active Galactic Nucleu (AGN) in NGC 2992, covering epochs ranging from 1978 to 2021, as well as new X-ray and optical spectra. The galaxy presents multiple Seyfert type transitions from Type 2 to intermediate-type, losing and regaining its Hα broad emission lines (BEL) recurrently. In X-rays, the source shows intrinsic variability with the absorption corrected luminosity varying by a factor of ∼ 40. We rule-out tidal disruption events or variable obscuration as causes of the type transitions, and show that the presence and the flux of th Hα BEL is directly correlated with the 2–10 keV X-ray luminosity (L2−10): the component disappears at L2−10 ≤ 2.6 × 1042 $\rm erg\, cm^{-2}\, s^{-1}$; this luminosity value translates into an Eddington ratio (λEdd) of ∼ 1 per cent. The λEdd in which the BEL transitions occur is the same as the critical value at which a state transition between a radiatively inefficient accretion flow and a thin accretion disk is expected, such similarity suggests that the AGN is operating at the threshold mass accretion rate between the two accretion modes. We find a correlation between the narrow Fe Kα flux and λEdd, and an anticorrelation between full-width at half maximum of Hα BEL and λEdd, in agreement with theoretical predictions. Two possible scenarios for type transitions are compatible with our results: either the dimming of the AGN continuum, which reduces the supply of ionizing photons available to excite the gas in the Broad Line Region (BLR), or the fading of the BLR structure itself occurs as the low accretion rate is not able to sustain the required cloud flow rate in a disc-wind BLR model.

中文翻译：

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NGC 2992 中与爱丁顿比率相关的“外观变化”事件

我们对 NGC 2992 中“变化的样子”（CL）活动银河核（AGN）的历史多波长发射进行了分析，涵盖了从 1978 年到 2021 年的时期，以及新的 X 射线和光谱。该星系呈现出从 2 型到中间型的多个 Seyfert 型转变，反复失去和重新获得其 Hα 宽发射线 (BEL)。在 X 射线中，源显示出内在的可变性，吸收校正光度变化约 40 倍。我们排除了潮汐破坏事件或变量遮蔽作为类型转换的原因，并表明 th 的存在和通量Hα BEL 与 2–10 keV X 射线光度 (L2−10) 直接相关：该分量在 L2−10 ≤ 2.6 × 1042 $\rm erg\, cm^{-2}\, s^{- 1}$; 这个光度值转化为大约 1% 的爱丁顿比 (λEdd)。发生 BEL 跃迁的 λEdd 与预期在辐射效率低的吸积流和薄吸积盘之间发生状态转换的临界值相同，这种相似性表明 AGN 在两种吸积模式。我们发现窄的 Fe Kα 通量和 λEdd 之间存在相关性，以及 Hα BEL 的半峰全宽和 λEdd 之间的反相关，与理论预测一致。类型转换的两种可能情况与我们的结果兼容：AGN连续体变暗，这减少了可用于激发宽线区域（BLR）中的气体的电离光子的供应，