Explaining the UV to X-ray correlation in AGN within the framework of X-ray illumination of accretion discs
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arXiv
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| Autori principali: | , , , , , |
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| Natura: | Preprint |
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2025
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| author | Kammoun, E. Papadakis, I. E. Dovčiak, M. Lusso, E. Nardini, E. Risaliti, G. |
| author_facet | Kammoun, E. Papadakis, I. E. Dovčiak, M. Lusso, E. Nardini, E. Risaliti, G. |
| contents | It is established that the ultraviolet (UV) and X-ray emissions in active galactic nuclei (AGN) are tightly correlated. This correlation is observed both in low- and high-redshift sources. In particular, observations of large samples of quasars revealed the presence of a non-linear correlation between UV and X-rays. The physical origin of this correlation is poorly understood. In this work, we explore this observed correlation in the framework of the X-ray illumination of the accretion disc by a central source. We have shown in previous works that this model successfully explains the continuum UV/optical time delays, variability, and the broadband spectral energy distribution in AGN. We use this model to produce $150,000$ model SEDs assuming a uniform distribution of model parameters. We compute the corresponding UV ($ 2500~Å $) and X-ray (2 keV) monochromatic luminosities and select only the model data points that agree with the observed UV-to-X-ray correlation. Our results show that the X-ray illumination of accretion disc model can reproduce the observed correlation for a subset of model configurations with a non-uniform distribution of black hole mass ($M_{\rm BH}$), accretion rate ($\dot{m}/\dot{m}_{\rm Edd}$), and power transferred from the accretion disc to the corona ($L_{\rm transf}/L_{\rm disc}$). In addition, our results reveal the presence of a correlation between $M_{\rm BH}$ and $\dot{m}/\dot{m}_{\rm Edd}$, and between $\dot{m}/\dot{m}_{\rm Edd}$ and $L_{\rm transf}/L_{\rm disc}$, to explain the observed X-ray-UV correlation. We also present evidence based on observed luminosities supporting our findings. We finally discuss the implications of our results. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2503_20770 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Explaining the UV to X-ray correlation in AGN within the framework of X-ray illumination of accretion discs Kammoun, E. Papadakis, I. E. Dovčiak, M. Lusso, E. Nardini, E. Risaliti, G. High Energy Astrophysical Phenomena It is established that the ultraviolet (UV) and X-ray emissions in active galactic nuclei (AGN) are tightly correlated. This correlation is observed both in low- and high-redshift sources. In particular, observations of large samples of quasars revealed the presence of a non-linear correlation between UV and X-rays. The physical origin of this correlation is poorly understood. In this work, we explore this observed correlation in the framework of the X-ray illumination of the accretion disc by a central source. We have shown in previous works that this model successfully explains the continuum UV/optical time delays, variability, and the broadband spectral energy distribution in AGN. We use this model to produce $150,000$ model SEDs assuming a uniform distribution of model parameters. We compute the corresponding UV ($ 2500~Å $) and X-ray (2 keV) monochromatic luminosities and select only the model data points that agree with the observed UV-to-X-ray correlation. Our results show that the X-ray illumination of accretion disc model can reproduce the observed correlation for a subset of model configurations with a non-uniform distribution of black hole mass ($M_{\rm BH}$), accretion rate ($\dot{m}/\dot{m}_{\rm Edd}$), and power transferred from the accretion disc to the corona ($L_{\rm transf}/L_{\rm disc}$). In addition, our results reveal the presence of a correlation between $M_{\rm BH}$ and $\dot{m}/\dot{m}_{\rm Edd}$, and between $\dot{m}/\dot{m}_{\rm Edd}$ and $L_{\rm transf}/L_{\rm disc}$, to explain the observed X-ray-UV correlation. We also present evidence based on observed luminosities supporting our findings. We finally discuss the implications of our results. |
| title | Explaining the UV to X-ray correlation in AGN within the framework of X-ray illumination of accretion discs |
| topic | High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2503.20770 |