解释宽发射线变化II：光度、特征尺寸和响应度之间的紧张关系
Interpreting broad emission-line variations II: Tensions between luminosity, characteristic size and responsivity
摘要：
我们调查的变化行为的广泛血红蛋白发射线，以驱动连续变化的最好的研究活动星系核NGC 5548。对于BLR几何形状的特定选择，基于光电离模型的Hb表面发射率，并使用13年光学连续光谱光变曲线的缩放版本作为驱动电离连续光谱的代理，我们探索了确定宽发射线光度L，特征尺寸R（RW）和可变幅度（即，以及它们之间的相互作用。对于固定边界模型，延伸到热尘的预测延迟血红蛋白平均太长。然而，血红蛋白的预测变异幅度提供了一个非常好的匹配，除了在低连续状态的观察。我们认为，驱动Hb表面发射率F（r）重新分布的连续通量变化本身不会导致R（RW）或eta（eff）的足够大的变化。因此，我们调查尘埃束缚的BLR的有效外边界的位置调制的连续水平和尘埃升华和尘埃凝结的时间尺度。我们发现，为了匹配所观察到的变异幅度宽血红蛋白在NGC 5548一个相当静态的外边界是首选。有趣的是，我们表明，最有效的方法，减少血红蛋白延迟，同时保持其响应度和等效宽度，是调用一个较小的值在入射电离光子通量Phi（H）为一个给定的电离源-云径向距离r，比通常推断从观察到的紫外线连续通量和典型的模型的连续SED。
英文摘要：
We investigate the variability behaviour of the broad Hb emission-line to driving continuum variations in the best-studied AGN NGC 5548. For a particular choice of BLR geometry, Hb surface emissivity based on photoionization models, and using a scaled version of the 13 yr optical continuum light curve as a proxy for the driving ionizing continuum, we explore several key factors that determine the broad emission line luminosity L, characteristic size R(RW), and variability amplitude (i.e., responsivity) eta, as well as the interplay between them. For fixed boundary models which extend as far as the hot-dust the predicted delays for Hb are on average too long. However, the predicted variability amplitude of Hb provides a remarkably good match to observations except during low continuum states. We suggest that the continuum flux variations which drive the redistribution in Hb surface emissivity F(r) do not on their own lead to large enough changes in R(RW) or eta(eff). We thus investigate dust-bounded BLRs for which the location of the effective outer boundary is modulated by the continuum level and the dust-sublimation and dust-condensation timescales. We find that in order to match the observed variability amplitude of broad Hb in NGC 5548 a rather static outer boundary is preferred. Intriguingly, we show that the most effective way of reducing the Hb delay, while preserving its responsivity and equivalent width, is to invoke a smaller value in the incident ionizing photon flux Phi(H) for a given ionizing source--cloud radial distance r, than is normally inferred from the observed UV continuum flux and typical models of the continuum SED.
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