The Global Implications of the Hard X-ray Excess in Type 1 AGN

TL;DR

This study investigates the widespread presence of a hard X-ray excess in type 1 AGN, suggesting it results from Compton-thick clouds near the broad line region, challenging reflection-based explanations.

Contribution

It provides the first comprehensive analysis of the hard X-ray excess in a large, local type 1 AGN sample, proposing a new model involving Compton-thick clouds for this phenomenon.

Findings

Hard X-ray excess is common in type 1 AGN

Most AGN show >50% coverage by Compton-thick gas

Sharp Fe K absorption edges indicate non-reflection origin

Abstract

Recent evidence for a strong 'hard excess' of flux at energies > 20 keV in some Suzaku observations of type 1 Active Galactic Nuclei (AGN) has motivated an exploratory study of the phenomenon in the local type 1 AGN population. We have selected all type 1 AGN in the Swift Burst Alert Telescope (BAT) 58-month catalog and cross-correlated them with the holdings of the Suzaku public archive. We find the hard excess phenomenon to be a ubiquitous property of type 1 AGN. Taken together, the spectral hardness and equivalent width of Fe K alpha emission are consistent with reprocessing by an ensemble of Compton-thick clouds that partially cover the continuum source. In the context of such a model, ~ 80 % of the sample has a hardness ratio consistent with > 50% covering of the continuum by low-ionization, Compton-thick gas. More detailed study of the three hardest X-ray spectra in our sample reveal a sharp Fe K absorption edge at ~ 7 keV in each of them, indicating that blurred reflection is not responsible for the very hard spectral forms. Simple considerations place the distribution of Compton-thick clouds at or within the optical broad line region.