A comprehensive analysis of the hard X-ray spectra of bright Seyfert galaxies

TL;DR

This study analyzed broad-band hard X-ray spectra of 28 bright Seyfert galaxies using multiple observatories, revealing that most have electron plasma temperatures below 100 keV and suggesting a compact X-ray emitting region.

Contribution

It provides the first comprehensive analysis of Seyfert galaxy spectra combining data from INTEGRAL, XMM-Newton, Suzaku, and RXTE with detailed Comptonization modeling.

Findings

Majority of Seyferts have electron plasma temperature below 100 keV.

Distribution of the Compton y parameter is bimodal.

Modest reflection and high flux ratio suggest a compact X-ray source geometry.

Abstract

Hard X-ray spectra of 28 bright Seyfert galaxies observed with INTEGRAL were analyzed together with the X-ray spectra from XMM-Newton, Suzaku and RXTE. These broad-band data were fitted with a model assuming a thermal Comptonization as a primary continuum component. We tested several model options through a fitting of the Comptonized continuum accompanied by a complex absorption and a Compton reflection. Both the large data set used and the model space explored allowed us to accurately determine a mean temperature kTe of the electron plasma, the Compton parameter y and the Compton reflection strength R for the majority of objects in the sample. Our main finding is that a vast majority of the sample (20 objects) is characterized by kTe < 100 keV, and only for two objects we found kTe > 200 keV. The median kTe for entire sample is 48(-14,+57) keV. The distribution of the y parameter is bimodal, with a broad component centered at ~0.8 and a narrow peak at ~1.1. A complex, dual absorber model improved the fit for all data sets, compared to a simple absorption model, reducing the fitted strength of Compton reflection by a factor of about 2. Modest reflection (median R ~0.32) together with a high ratio of Comptonized to seed photon fluxes point towards a geometry with a compact hard X-ray emitting region well separated from the accretion disc. Our results imply that the template Seyferts spectra used in AGN population synthesis models should be revised.