# X-ray variability of AGN and correlations with spectral properties

Source: [X-ray variability of AGN and correlations with spectral properties](<https://www.sota2.com/research/paper/68fa24f22c2a3760193aaef0>)

Collection index: [llms.txt](<https://www.sota2.com/research/llms.txt>)

Data updated: 2025-10-24T09:40:52.177Z

Authors: K. Nandra

Published: 2000-12-20T20:54:29.000Z

## Abstract

Rapid flux changes in the X-ray emission from active galactic nuclei are commonly observed. The power-density spectra show a pseudo power-law form with a turnover at low frequencies and a high frequency break, similar to galactic black-hole candidates. There have been a few claims for periodicities but these are not a well-established property of the class. The amplitude of variability depends on a number of source parameters, including luminosity and spectral properties. The variability amplitude is correlated with X-ray spectral index, and anti-correlated with the width of the permitted optical lines. In one particularly well-observed case, NGC 7469, we see a relationship between the X-ray and UV variability, which indicates that the dominant emission process for the X-rays is thermal Comptonization. Variations in the X-ray emission are related to changes in the UV seed photons, but it appears there must also be a mechanism - perhaps that which heats the Comptonizing corona - that induces rapid variability intrinsic to the X-rays.

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## Original sources and implementation

[Original paper](<https://arxiv.org/abs/astro-ph/0012448>)

[PDF](<https://arxiv.org/pdf/astro-ph/0012448.pdf>)