Multiwavelength properties of changing-state active galactic nuclei

Changing-state active galactic nuclei (CSAGNs) exhibit rapid variability; their mass accretion rates can change by several orders of magnitude in a few years. This provides us with a unique opportunity to study the evolution of the inner accretion flow almost in real time. Here we used over 1000 observations to study the broadband X-ray spectra of a sample of five CSAGNs, spanning three orders of magnitude in Eddington ratio ( λ Edd ), using phenomenological models to trace the evolution of key spectral components. We derive several fundamental parameters, such as the photon index, soft excess strength, reflection strength, and luminosities of the soft excess and primary continuum. We find that the soft excess and primary continuum emissions show a very strong positive correlation ( p ≪ 10 −10 ), suggesting a common physical origin. The soft excess strength does not show any dependence on the reflection parameter, suggesting that in these objects the soft excess is not dominated by a blurred ionized reflection process. On the other hand, the strength of the soft excess is found to be strongly positively correlated with the Eddington ratio ( p ≪ 10 −10 ), and we find that the soft excess vanishes below log λ Edd ∼ −2.5. Moreover, we find a clear V-shaped relation for Γ − λ Edd , with a break at log λ Edd = −2.47 ± 0.09. Our findings indicate a change in the geometry of the inner accretion flow at low Eddington ratios, and that the soft excess is primarily produced via warm Comptonization.

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Publication Details

Journal
Astronomy and Astrophysics
Published
2026-01-30
DOI
https://doi.org/10.1051/0004-6361/202556654
Primary Topic
Astrophysical Phenomena and Observations
Type
article
Field-Weighted Citation Impact
0.00

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article

Multiwavelength properties of changing-state active galactic nuclei

Kristína Kallová, Elena Shablovinskaya, George Dimopoulos, Dragana Illic et al.
Astronomy and Astrophysics
Astrophysical Phenomena and Observations
article

Multiwavelength properties of changing-state active galactic nuclei

Kristína Kallová, Elena Shablovinskaya, George Dimopoulos, Dragana Illic, Hsian-Kuang Chang, Arghajit Jana, Michael Koss, Alessia Tortosa, Benny Trakhtenbrot, Claudio Ricci, Franz E. Bauer, Matthew J. Temple, Yaherlyn Diaz, Kriti Kamal Gupta
article en

Abstract

Changing-state active galactic nuclei (CSAGNs) exhibit rapid variability; their mass accretion rates can change by several orders of magnitude in a few years. This provides us with a unique opportunity to study the evolution of the inner accretion flow almost in real time. Here we used over 1000 observations to study the broadband X-ray spectra of a sample of five CSAGNs, spanning three orders of magnitude in Eddington ratio ( λ Edd ), using phenomenological models to trace the evolution of key spectral components. We derive several fundamental parameters, such as the photon index, soft excess strength, reflection strength, and luminosities of the soft excess and primary continuum. We find that the soft excess and primary continuum emissions show a very strong positive correlation ( p ≪ 10 −10 ), suggesting a common physical origin. The soft excess strength does not show any dependence on the reflection parameter, suggesting that in these objects the soft excess is not dominated by a blurred ionized reflection process. On the other hand, the strength of the soft excess is found to be strongly positively correlated with the Eddington ratio ( p ≪ 10 −10 ), and we find that the soft excess vanishes below log λ Edd ∼ −2.5. Moreover, we find a clear V-shaped relation for Γ − λ Edd , with a break at log λ Edd = −2.47 ± 0.09. Our findings indicate a change in the geometry of the inner accretion flow at low Eddington ratios, and that the soft excess is primarily produced via warm Comptonization.

Astronomy and AstrophysicsVol. 707
University of Geneva (CH), Space Science Institute (US), University of Liège (BE), Universität Hamburg (DE), Tel Aviv University (IL), University of Tarapacá (CL), Durham University (GB), National Tsing Hua University (TW), Astronomical Observatory of Rome (IT), Ghent University (BE), University of Belgrade (RS), Max Planck Institute for Extraterrestrial Physics (DE), Excellence Cluster Origins (DE), SRM University, Andhra Pradesh (IN), Institute of Astronomy (RU), SRM University (IN), Hamburg Institut (Germany) (DE), Eureka Scientific (US), Max Planck Institute for Radio Astronomy (DE), National Institute for Astrophysics (IT), Universidad Diego Portales (CL)
Smithsonian Institution, National Aeronautics and Space Administration, Alexander von Humboldt-Stiftung, California Institute of Technology, UK Research and Innovation, European Space Agency, University of Leicester, European Commission, Deutsche Forschungsgemeinschaft, Schweizerischer Nationalfonds zur Förderung der Wissenschaftlichen Forschung, Belgian Federal Science Policy Office, Nuclear Safety and Security Commission, Pontificia Universidad Católica de Chile, Agencia Nacional de Investigación y Desarrollo, National Science and Technology Council, Goddard Space Flight Center, Smithsonian Astrophysical Observatory, Japan Aerospace Exploration Agency, Astrophysics Science Division, Astrophysics Division
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