AGN's UV and X-ray luminosities in clumpy accretion flows

TL;DR

This paper proposes that shocks in inhomogeneous accretion flows around black holes in AGNs can explain their UV and X-ray emissions, with a cascade of shocks producing observed luminosity ratios and spectral features.

Contribution

It introduces a simple analytical model linking shock cascades in clumpy accretion flows to AGN UV and X-ray emissions, explaining observed luminosity ratios and spectral correlations.

Findings

Shocks in clumpy accretion flows can produce UV and X-ray emissions.

The X-ray to UV luminosity ratio is less than one and varies with black hole mass.

The model aligns with observed $ ext{L}_X/ ext{L}_{UV}$ ratios and the $ ext{α}_{OX}-l_{UV}$ anticorrelation.

Abstract

We consider the fuelling of the central massive black hole in Active Galactic Nuclei, through an inhomogeneous accretion flow. Performing simple analytical treatments, we show that shocks between elements (clumps) forming the accretion flow may account for the UV and X-ray emission in AGNs. In this picture, a cascade of shocks is expected, where optically thick shocks give rise to optical/UV emission, while optically thin shocks give rise to X-ray emission. The resulting blue bump temperature is found to be quite similar in different AGNs. We obtain that the ratio of X-ray luminosity to UV luminosity is smaller than unity, and that this ratio is smaller in massive objects compared to less massive sources. This is in agreement with the observed $L_{X}/L_{UV}$ ratio and suggests a possible interpretation of the $\alpha_{OX}-l_{UV}$ anticorrelation.