Using Faded Changing-Look Quasars to Unveil the Spectral Energy Distribution Evolution of Low-Luminosity Active Galactic Nuclei

Olivier Gilbert; John J. Ruan; Laura Duffy; Michael Eracleous; Scott F. Anderson; Paul J. Green; Daryl Haggard; Richard M. Plotkin; Jessie C. Runnoe; Malgorzata Sobolewska

arXiv · 2508.01933

Using Faded Changing-Look Quasars to Unveil the Spectral Energy Distribution Evolution of Low-Luminosity Active Galactic Nuclei

Olivier Gilbert·John J. Ruan·Laura Duffy·Michael Eracleous·Scott F. Anderson·Paul J. Green·Daryl Haggard·Richard M. Plotkin·Jessie C. Runnoe·Malgorzata Sobolewska

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Abstract

The structure of accretion flows in low-luminosity active galactic nuclei (AGN) at low Eddington ratios (~10^-2 to 10^-3) are poorly-understood, and can be probed using the spectral energy distributions (SEDs) of faded changing-look (CL) quasars. Previous results using single-epoch X-ray and rest-frame UV observations of samples of faded CL quasars suggest that their SED properties at low Eddington ratios display similarities to X-ray binaries fading from outburst. However, more robust tests demand multi-epoch observations that can trace the temporal behavior of the SEDs of individual AGN at low Eddington ratios. Here, we perform this test, by obtaining a second epoch of UV and X-ray observations of a sample of three faded CL quasars with bolometric Eddington ratios of <10^-3, using a combination of contemporaneous HST UV imaging, Chandra X-ray observations, and optical spectroscopy. We find that all three CL quasars varied in luminosity, and their optical-to-X-ray spectral indices alpha_OX all individually display a negative (harder-when-brighter) correlation with Eddington ratio. This SED evolution is also often observed in X-ray binaries at low Eddington ratios, and adds to the growing evidence that AGN accretion flows behave analogously to X-ray binaries across all accretion states.

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Olivier Gilbert, John J. Ruan, Laura Duffy, Michael Eracleous, Scott F. Anderson, Paul J. Green, Daryl Haggard, Richard M. Plotkin, Jessie C. Runnoe, Malgorzata Sobolewska. 2025-08-03. Using Faded Changing-Look Quasars to Unveil the Spectral Energy Distribution Evolution of Low-Luminosity Active Galactic Nuclei. https://arxiv.org/abs/2508.01933

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