Changing-look Active Galactic Nuclei from the Dark Energy Spectroscopic Instrument. VII. Testing Disk-Corona Diagnostics with eROSITA

@misc{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},
  howpublished = {arXiv},
  year = {2026},
  month = oct,
  doi = {10.48550/arxiv.2610.10331},
  eprint = {2610.10331},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2610.10331},
}

TY  - UNPB
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  - 2026/10/07
PB  - arXiv
DO  - 10.48550/arxiv.2610.10331
UR  - https://arxiv.org/abs/2610.10331
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, α_OX, and the Eddington ratio, λ_Edd≡ L_bol/L_Edd. 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 α_OX and the optical-continuum-based Eddington ratio, λ_Edd,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 α_OX on ultraviolet luminosity and by the covariance between the rest-frame 2500 Angstrom luminosity, L_2500, the black-hole mass, M_BH, and λ_Edd,opt. When an X-ray-based Eddington ratio is used instead, the relation reverses sign because the X-ray luminosity, L_X, enters the two axes with opposite signs. An apparent α_OX-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, Γ_eff, 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.
ER  -