Seyfert galaxies in the local Universe (z$\leq$ 0.1): the average X-ray spectrum as seen by $BeppoSAX$

TL;DR

This study analyzes the average X-ray spectra of 105 nearby Seyfert galaxies using BeppoSAX data, confirming key aspects of the unified AGN model and identifying spectral correlations.

Contribution

It provides a homogeneous analysis of Seyfert galaxy X-ray spectra, measuring average spectral parameters and testing unified scheme assumptions with a large, high-quality dataset.

Findings

Average photon index ~1.8

High-energy cut-off ~290 keV

Reflection component R ~1.0

Abstract

The $BeppoSAX$ archive is currently the largest reservoir of high sensitivity simultaneous soft and hard-X ray data of Seyfert galaxies. From this database all the Seyfert galaxies (105 objects of which 43 are type I and 62 are type II) with redshift lower than 0.1 have been selected and analyzed in a homogeneous way (Dadina 2007). The X-ray data so collected allow to infer the average spectral properties of nearby Seyfert galaxies included in the original sample and, most notably: the photon index ($\Gamma$$\sim$1.8), the high-energy cut-off (Ec$\sim$290 keV), and the relative amount of reflection (R$\sim$1.0). The data have been also used to test some assumptions of the unified scheme for the AGN. The distributions of the isotropic indicators (photon index, relative amount of reflection, high-energy cut-off and narrow FeK$\alpha$ energy centroid) are similar in type I and type II objects while the absorbing column and the iron line equivalent width significantly differ between the two classes of active galactic nuclei. Confirming previous results, the narrow FeK$\alpha$ line is consistent, in Seyfert 2, with being produced in the same matter responsible for the observed obscuration. These results, thus, support the basic picture of the unified model. Moreover, the presence of a X-ray Baldwin effect in Seyfert 1 has been here measured using the 20-100 keV luminosity (EW$\propto$L(20-100)$^{-0.22\pm0.05}$). Finally, the possible presence of a correlation between the photon index and the amount of reflection is confirmed thus indicating thermal Comptonization as the most likely origin of the high energy emission for the active galactic nuclei included in the original sample.