Coevolution of broad emission lines and X-ray spectrum in changing-look AGNs

Abstract

Changing-look active galactic nuclei (CLAGNs) show the disappearance and reappearance of broad emission lines in a few years, which challenges the orientation-based AGN unification model. We reduce the X-ray data for five well-studied CLAGNs that show a strong change in broad emission lines in the past several decades. We find that the X-ray photon index, $\Gamma$, and the Eddington-scaled X-ray luminosity, $L_{2-10keV}/L_{\mathrm{Edd}}$, normally follow negative and positive correlations when the Eddington ratio is lower and higher than a critical value of $\sim 10^{-3}$. We find that the CLAGNs observed with broad H$\beta$ emission lines stay in the positive part of the $\Gamma -L_{2-10keV}/L_{\mathrm{Edd}}$ correlation, while the broad H$\beta$ lines become weak or disappear in the anticorrelation part of the $\Gamma -L_{2-10keV}/L_{\mathrm{Edd}}$ correlation, which suggests that the evolution of the broad lines should be correlated with the evolution of the underlying accretion process. We further find that the CLAGNs are consistent with the other different types of AGNs in the $L_{\mathrm{bol}}-L_{\mathrm{bol}}/L_{\mathrm{Edd}}$ correlation. These results support that the CLAGNs are belong to a special stage of AGNs with a bolometric Eddington ratio $\sim$1\%, where the broad emission lines are easily affected by the strong variation in ionization luminosity that is caused by the transition of accretion modes.

published paper of 2022 ApJ, 930,46

References in corpus (17)

• The Discovery of the First "Changing Look" Quasar: New Insights into the Physics & Phenomenology of AGN
• Radiatively Inefficient Accretion in Nearby Galaxies
• AGN Type-casting: Mrk 590 No Longer Fits the Role
• Mid-infrared variability of changing-look AGN
• The hard X-ray spectral evolution in X-ray binaries and its application to constrain the black hole mass of ultraluminous X-ray sources
• The Close AGN Reference Survey (CARS) - Mrk 1018 returns to the shadows after 30 years as a Seyfert 1
• An accretion disc-corona model for X-ray spectra of active galactic nuclei
• Long-term optical spectral monitoring of a changing-look AGN NGC 3516 I: Continuum and broad-line flux variability
• Accretion Disk Spectra of the Brightest Ultra-luminous X-ray Source in M82
• The Eddington ratio-dependent changing look events in NGC 2992
• Changing-look event in NGC 3516: continuum or obscuration variability?
• Broadband X-Ray Observations of the 2018 Outburst of the Changing-Look Active Galactic Nucleus NGC 1566
• A flare in the optical spotted in the changing-look Seyfert NGC 3516
• Long-term and multi-wavelength evolution of a changing-look AGN Mrk 1018
• The post-maximum behaviour of the changing-look Seyfert galaxy NGC 1566
• Spectropolarimetry of the changing-look active galactic nucleus Mrk 1018
• A detailed analysis of the high resolution X-ray spectra of NGC 3516: Variability of the ionized absorbers

Cited by in corpus (3)

• BASS XXXIX: Swift-BAT AGN with changing-look optical spectra
• Flares in the changing look AGN Mrk 590. I: The UV response to X-ray outbursts suggests a more complex reprocessing geometry than a standard disk
• Investigating Non-linear and Stochastic Hard X-ray Variability of Active Galactic Nuclei using Recurrence Analysis