Could the Interband Lag of Active Galactic Nucleus Vary Randomly?

Abstract The interband lags among the optical broad-band continua of active galactic nuclei (AGNs) have been intensively explored over the past decade. However, the nature of the lags remains under debate. Here, utilizing two distinct scenarios for AGN variability, i.e., the thermal fluctuation of accretion disk and the reprocessing of both the accretion disk and clouds in the broad line region, we show that, owing to the random nature of AGN variability, the interband lags of an individual AGN would vary from one campaign with a finite baseline to another. Specifically, the thermal fluctuation scenario implies larger variations in the lags than the reprocessing scenario. Moreover, the former predicts a positive correlation between the lag and variation amplitude, while the latter does not result in such a correlation. For both scenarios, averaging the lags of an individual AGN measured with repeated and nonoverlapping campaigns would give rise to a stable lag, which is larger for a longer baseline and gets to saturation for a sufficiently long baseline. However, obtaining the stable lag for an individual AGN is very time-consuming. Alternatively, it can be equivalently inferred by averaging the lags of a sample of AGNs with similar physical properties, and thus can be properly compared with predictions of AGN models. In addition, several new observational tests suggested by our simulations are discussed, as well as the role of the deep high-cadence surveys of the Wide Field Survey Telescope in enriching our knowledge of the lags.

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Publication Details

Journal
The Astrophysical Journal
Published
2024-11-20
DOI
https://doi.org/10.3847/1538-4357/ad86bc
Citations
7
Primary Topic
Astrophysical Phenomena and Observations
Type
article
Field-Weighted Citation Impact
2.32

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article

Could the Interband Lag of Active Galactic Nucleus Vary Randomly?

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7 citations
The Astrophysical Journal
Astrophysical Phenomena and Observations
2.32
article

Could the Interband Lag of Active Galactic Nucleus Vary Randomly?

Lulu Fan, Zhicheng He, Wen Zhao, Ji-an Jiang, Junxian Wang, Xu Fan Hu, Zizhao He, Teng Liu, Zhen-Yi Cai, Yongquan Xue, Min-Xuan Cai, Zhenfeng Sheng, Hengxiao Guo, Tinggui Wang, Wen-Yong Kang, Zhengyan Liu, Mouyuan Sun, Lei Lei, Guilin Liu, Ning Jiang, Zhen-Bo Su
article en
7 citations

Abstract

Abstract The interband lags among the optical broad-band continua of active galactic nuclei (AGNs) have been intensively explored over the past decade. However, the nature of the lags remains under debate. Here, utilizing two distinct scenarios for AGN variability, i.e., the thermal fluctuation of accretion disk and the reprocessing of both the accretion disk and clouds in the broad line region, we show that, owing to the random nature of AGN variability, the interband lags of an individual AGN would vary from one campaign with a finite baseline to another. Specifically, the thermal fluctuation scenario implies larger variations in the lags than the reprocessing scenario. Moreover, the former predicts a positive correlation between the lag and variation amplitude, while the latter does not result in such a correlation. For both scenarios, averaging the lags of an individual AGN measured with repeated and nonoverlapping campaigns would give rise to a stable lag, which is larger for a longer baseline and gets to saturation for a sufficiently long baseline. However, obtaining the stable lag for an individual AGN is very time-consuming. Alternatively, it can be equivalently inferred by averaging the lags of a sample of AGNs with similar physical properties, and thus can be properly compared with predictions of AGN models. In addition, several new observational tests suggested by our simulations are discussed, as well as the role of the deep high-cadence surveys of the Wide Field Survey Telescope in enriching our knowledge of the lags.

The Astrophysical JournalVol. 976(2)
University of Science and Technology of China (CN), Shanghai Jiao Tong University (CN), Xiamen University (CN), Shanghai Astronomical Observatory (CN), Purple Mountain Observatory (CN), Geological Exploration Technology Institute of Jiangsu Province (CN)
National Science Foundation, National Natural Science Foundation of China, National Key Research and Development Program of China, Fundamental Research Funds for the Central Universities
Openalex Percentile: Top 12%
Astrophysical Phenomena and Observations
2.32
DOIOpen Access PDFOpenAlex
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