The X-ray spectral properties of the AGN population in the XMM-Newton bright serendipitous survey

TL;DR

This study provides a comprehensive X-ray spectral analysis of over 300 AGN from the XMM-Newton bright survey, revealing correlations between spectral properties, luminosity, and AGN types, and exploring spectral features like the soft excess and Fe Kalpha line.

Contribution

It offers the first detailed spectral analysis of a large, diverse AGN sample, combining individual and average spectra to understand spectral features and their dependence on luminosity and type.

Findings

Anti-correlation between spectral index and luminosity.

Intrinsic absorption distribution aligns with AGN unified schemes.

Detection of the Iwasawa-Taniguchi effect with decreasing Fe Kalpha EW at higher luminosities.

Abstract

We present here a detailed X-ray spectral analysis of the AGN belonging to the XMM-Newton bright survey (XBS) that comprises more than 300 AGN up to redshift ~ 2.4. We performed an X-ray analysis following two different approaches: by analyzing individually each AGN X-ray spectrum and by constructing average spectra for different AGN types. From the individual analysis, we find that there seems to be an anti correlation between the spectral index and the sources' hard X-ray luminosity, such that the average photon index for the higher luminosity sources (> 10E44 erg/s) is significantly flatter than the average for the lower luminosity sources. We also find that the intrinsic column density distribution agrees with AGN unified schemes, although a number of exceptions are found (3% of the whole sample), which are much more common among optically classified type 2 AGN. We also find that the so-called "soft-excess", apart from the intrinsic absorption, constitutes the principal deviation from a power-law shape in AGN X-ray spectra and it clearly displays different characteristics, and likely a different origin, for unabsorbed and absorbed AGN. Regarding the shape of the average spectra, we find that it is best reproduced by a combination of an unabsorbed (absorbed) power law, a narrow Fe Kalpha emission line and a small (large) amount of reflection for unabsorbed (absorbed) sources. We do not significantly detect any relativistic contribution to the line emission and we compute an upper limit for its equivalent width (EW) of 230 eV at the 3 sigma confidence level. Finally, by dividing the type 1 AGN sample into high- and low-luminosity sources, we marginally detect a decrease in the narrow Fe Kalpha line EW and in the amount of reflection as the luminosity increases, the "so-called" Iwasawa-Taniguchi effect.