2019/12/09 by Hao Liu, Qingwen Wu, liu, Hao +5
Physics and Astronomy · #Astronomy and Astrophysical Research #Astrophysical Phenomena and Observations #Astrophysics of Galaxies (astro-ph.GA) #FOS: Physical sciences #Galaxies: Formation, Evolution, Phenomena
paper · pdf · doi:10.48550/arxiv.1912.03972
openalex publication_date 2019/12/09 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
The discovery of changing-look active galactic nuclei (CL AGNs), with appearance and disappearance of broad emission lines and/or with strong variation of line-of-sight column density within a few years, challenges the AGN unification model. We explore the physical mechanisms based on the X-ray spectral evolution for a sample of 15 CL AGNs. We find that the X-ray photon index, Γ, and Eddington-scaled X-ray luminosity, L\rm 2-10 keV/L\rm Edd, follow negative and positive correlations when L\rm 2-10 keV/L\rm Edd is lower and higher than a critical value of ∼ 10-3. This different X-ray spectral evolution is roughly consistent with the prediction of the accretion-mode transition (e.g., clumpy cold gas or cold disk to advection dominated accretion flow, or vice visa). With quasi-simultaneous X-ray and optical spectrum observations within one year, we find that the CL AGNs observed with and without broad emission lines stay in the positive and negative part of the Γ-L\rm 2-10 keV/L\rm Edd correlation respectively. Our result suggest that the change of the accretion mode may be the physical reason for the CL AGNs.