Issue |
A&A
Volume 697, May 2025
|
|
---|---|---|
Article Number | A55 | |
Number of page(s) | 11 | |
Section | Extragalactic astronomy | |
DOI | https://doi.org/10.1051/0004-6361/202452629 | |
Published online | 06 May 2025 |
Explaining the UV to X-ray correlation in active galactic nuclei within the framework of X-ray illumination of accretion discs
1
Dipartimento di Matematica e Fisica, Università Roma Tre, Via della Vasca Navale 84, I-00146 Rome, Italy
2
INAF – Osservatorio Astrofisico di Arcetri, Largo Enrico Fermi 5, I-50125 Firenze, Italy
3
Cahill Center for Astrophysics, California Institute of Technology, 1216 East California Boulevard, Pasadena, CA 91125, USA
4
Department of Physics and Institute of Theoretical and Computational Physics, University of Crete, 71003 Heraklion, Greece
5
Institute of Astrophysics, FORTH, GR-71110 Heraklion, Greece
6
Astronomical Institute of the Czech Academy of Sciences, Boční II 1401, CZ-14100 Prague, Czech Republic
7
Dipartamento di Fisica e Astronomia, Università di Firenze, Via G. Sansone 1, I-50019 Sesto Fiorentino, FI, Italy
⋆ Corresponding author; ekammoun.astro@gmail.com
Received:
15
October
2024
Accepted:
25
March
2025
Context. It is established that the ultraviolet (UV) and X-ray emission in active galactic nuclei (AGN) is tightly correlated. This correlation is observed both in low- and high-redshift sources. In particular, observations of large samples of quasars revealed a non-linear correlation between UV and X-rays. The physical origin of this correlation is poorly understood.
Aims. We explore this observed correlation in the framework of the X-ray illumination of the accretion disc by a central source. We showed previously that this model successfully explains the continuum UV/optical time delays, variability, and the broadband spectral energy distribution in AGN.
Methods. We used this model to produce 150 000 model spectral energy distributions, assuming a uniform distribution of the model parameters. We computed the corresponding UV (2500 Å) and X-ray (2 keV) monochromatic luminosities and selected only the model data points that agreed with the observed UV-to-X-ray correlation.
Results. Our results show that the X-ray illuminated accretion disc model can reproduce the observed correlation for a subset of model configurations with a non-uniform distribution of the black hole mass (MBH), accretion rate (ṁ/ṁEdd), and power transferred from the accretion disc to the corona (Ltransf/Ldisc). In addition, our results reveal a correlation between MBH and ṁ/ṁEdd and between ṁ/ṁEdd and Ltransf/Ldisc that explains the observed X-ray-UV correlation. We also present evidence based on observed luminosities that supports our findings. We finally discuss the implications of our results.
Key words: accretion / accretion disks / galaxies: active / galaxies: nuclei / quasars: general / quasars: supermassive black holes
© The Authors 2025
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
This article is published in open access under the Subscribe to Open model. Subscribe to A&A to support open access publication.
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.