Dependency of Optical/UV parameters on X-ray spectral index in AGNs

TL;DR

This study investigates the relationship between X-ray spectral index and optical parameters in AGNs, finding no evolution of the spectral index with redshift and suggesting it is influenced by soft excess and reflection components.

Contribution

It provides a large-scale analysis of the spectral index evolution across redshift and its lack of correlation with optical features in AGNs, clarifying previous degeneracies.

Findings

No change in spectral index $B3$ across redshift.

Spectral index $B3$ shows no correlation with optical parameters.

$B3$ influenced by soft excess and reflection components.

Abstract

The study of Active Galactic Nuclei (AGNs) is vital in order to understand their respective nuclei bounded activity primarily triggered by the accretion disk and the associated corona. The hard X-ray emission characterised by the spectral index $\Gamma$ emitted by these sources in 2-10 keV band ionizes the nearby physical features like disk, BLR, NLR and provides a radiative configuration. However, based on previous studies, there is degeneracy in the evolution of $\Gamma$ across the redshift, wherein few studies display a systematic trend in the evolution and others rule out the systematic variation. In the present work, we study the evolution of $\Gamma$ across the redshift for a very large sample and perform further studies on the variation of $\Gamma$ with optical parameters using SDSS data viz. H$_{\beta}$ \& Mg II and their luminosities. Based on analysis we find that there is no change in $\Gamma$ across the redshift and it does not show any correlation with the optical parameters. This strongly suggests that the $\Gamma$ is influenced by the soft excess and/or reflection component and is affecting the disk and BLR region at the same strength across the redshift.