Changing-look Active Galactic Nuclei from the Dark Energy Spectroscopic Instrument. VII. Testing Disk–Corona Diagnostics with eROSITA
- 1Durham University Centre for Extragalactic Astronomy, Department of Physics, , South Road, Durham, DH1 3LE ,
- 2National Astronomical Observatories, Chinese Academy of Sciences , 20A Datun Road, Chaoyang District, Beijing 100101 ,
Abstract
Changing-look active galactic nuclei (CL-AGN) have been proposed to follow an X-ray-binary-like, V-shaped relation between the optical/ultraviolet-to-X-ray spectral slope, αOX, and the Eddington ratio, λEdd ≡ Lbol/LEdd. We test this interpretation using CL-AGN selected from the Dark Energy Spectroscopic Instrument (DESI) and control samples matched to the eROSITA all-sky survey (eRASS). We find that the apparent positive correlation between αOX and the optical-continuum-based Eddington ratio, λEdd, opt, is not unique to CL-AGN, but also appears in matched non-changing-look samples. In broad-Hα AGN, our main statistical sample, this structure is largely driven by the known dependence of αOX on ultraviolet luminosity and by the covariance between the rest-frame 2500 Å luminosity, L2500, the black-hole mass, MBH, and λEdd, opt. When an X-ray-based Eddington ratio is used instead, the relation reverses sign because the X-ray luminosity, LX, enters the two axes with opposite signs. An apparent αOX–Eddington-ratio V-shape can therefore be induced by the luminosity estimator and is not a standalone accretion-state diagnostic. As a complementary test, we examine the eRASS effective photon index, Γeff, inferred from catalogue band fluxes. In broad-line AGN, it shows a weak positive association with the X-ray-independent optical Eddington ratio. However, the weaker hard-band trend depends on the null model and does not isolate coronal softening. These results motivate further X-ray spectroscopy, combined with independently estimated Eddington ratios, to test for intrinsic changes in the disk–corona system.
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BibTeX
@article{guo2026changinglook,
title = {{Changing-look Active Galactic Nuclei from the Dark Energy Spectroscopic Instrument. VII. Testing Disk–Corona Diagnostics with eROSITA}},
author = {Wei-Jian Guo and Shuo Zhai and Zhu-Heng Yao and Huaqing Cheng and Jingwei Hu and Jun-Jie Jin},
journal = {Monthly Notices of the Royal Astronomical Society},
year = {2026},
month = oct,
doi = {10.1093/mnras/stag1920},
url = {https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/stag1920/8910745},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Changing-look Active Galactic Nuclei from the Dark Energy Spectroscopic Instrument. VII. Testing Disk–Corona Diagnostics with eROSITA
AU - Wei-Jian Guo
AU - Shuo Zhai
AU - Zhu-Heng Yao
AU - Huaqing Cheng
AU - Jingwei Hu
AU - Jun-Jie Jin
PY - 2026
DA - 2026/10/12
JO - Monthly Notices of the Royal Astronomical Society
DO - 10.1093/mnras/stag1920
UR - https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/stag1920/8910745
AB - Changing-look active galactic nuclei (CL-AGN) have been proposed to follow an X-ray-binary-like, V-shaped relation between the optical/ultraviolet-to-X-ray spectral slope, αOX, and the Eddington ratio, λEdd ≡ Lbol/LEdd. We test this interpretation using CL-AGN selected from the Dark Energy Spectroscopic Instrument (DESI) and control samples matched to the eROSITA all-sky survey (eRASS). We find that the apparent positive correlation between αOX and the optical-continuum-based Eddington ratio, λEdd, opt, is not unique to CL-AGN, but also appears in matched non-changing-look samples. In broad-Hα AGN, our main statistical sample, this structure is largely driven by the known dependence of αOX on ultraviolet luminosity and by the covariance between the rest-frame 2500 Å luminosity, L2500, the black-hole mass, MBH, and λEdd, opt. When an X-ray-based Eddington ratio is used instead, the relation reverses sign because the X-ray luminosity, LX, enters the two axes with opposite signs. An apparent αOX–Eddington-ratio V-shape can therefore be induced by the luminosity estimator and is not a standalone accretion-state diagnostic. As a complementary test, we examine the eRASS effective photon index, Γeff, inferred from catalogue band fluxes. In broad-line AGN, it shows a weak positive association with the X-ray-independent optical Eddington ratio. However, the weaker hard-band trend depends on the null model and does not isolate coronal softening. These results motivate further X-ray spectroscopy, combined with independently estimated Eddington ratios, to test for intrinsic changes in the disk–corona system.
SN - 0035-8711
SN - 1365-2966
ER -