Frequency-resolved Lags in UV/Optical Continuum Reverberation Mapping
Frequency-resolved Lags in UV/Optical Continuum Reverberation Mapping
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DOI：
10.3847/1538-4357/ac3913
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发表时间：
2021-09
期刊：
影响因子：
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通讯作者：
E. Cackett;A. Zoghbi;O. Ulrich
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作者：
E. Cackett;A. Zoghbi;O. Ulrich
近年来，涉及附近活动星系核高节奏紫外线/光学监测活动的连续混响测绘已被用来推断其吸积盘的大小。这些活动的主要结果之一是，在许多情况下，吸积盘显得太大，是标准模型的 2-3 倍。部分原因可能是由于宽线区域 (BLR) 的扩散连续谱发射，巴尔默跳跃周围的过度滞后表明了这一点。标准互相关滞后分析技术通常仅用于恢复峰值或质心滞后，并且无法轻松区分来自磁盘的重新处理和来自 BLR 的重新处理。然而，频率分辨滞后分析（其中滞后是在每个傅立叶频率处确定的）有可能在不同尺寸尺度上分离出再处理。在这里，我们通过模拟来证明该方法的潜力，然后应用最大似然方法来确定 NGC 5548 中的频率分辨滞后。我们发现，NGC 5548 中的滞后通常会随着频率的增加而平滑减小，并且单独通过吸积盘再处理很难描述。标准互相关滞后与频率低于 0.1 天−1 的滞后一致，表明它们主要来自尺寸尺度大于 ∼10 光天的再处理。与 BLR 一致的更远的再处理器与标准尺寸吸积盘的组合比单独使用较大的吸积盘更符合观察到的滞后。
In recent years, continuum-reverberation mapping involving high-cadence UV/optical monitoring campaigns of nearby active galactic nuclei has been used to infer the size of their accretion disks. One of the main results from these campaigns has been that in many cases the accretion disks appear too large, by a factor of 2–3, compared to standard models. Part of this may be due to diffuse continuum emission from the broad-line region (BLR), which is indicated by excess lags around the Balmer jump. Standard cross-correlation lag-analysis techniques are usually used to just recover the peak or centroid lag and cannot easily distinguish between reprocessing from the disk and BLR. However, frequency-resolved lag analysis, where the lag is determined at each Fourier frequency, has the potential to separate out reprocessing on different size scales. Here we present simulations to demonstrate the potential of this method and then apply a maximum-likelihood approach to determine frequency-resolved lags in NGC 5548. We find that the lags in NGC 5548 generally decrease smoothly with increasing frequency, and are not easily described by accretion-disk reprocessing alone. The standard cross-correlation lags are consistent with lags at frequencies lower than 0.1 day−1, indicating they are dominated from reprocessing at size scales greater than ∼10 light days. A combination of a more distant reprocessor, consistent with the BLR, along with a standard-sized accretion disk is more consistent with the observed lags than a larger disk alone.