The Suzaku View of the Swift/BAT AGNs (II): Time Variability and Spectra of Five "Hidden" AGNs

TL;DR

This study uses simultaneous Suzaku X-ray spectra to analyze five candidate 'hidden' AGNs from the Swift/BAT survey, revealing they are not Compton-thick and exploring variability-luminosity correlations.

Contribution

First simultaneous Suzaku observations of these AGNs provide clearer spectral analysis, improving understanding of their true absorption states and variability characteristics.

Findings

Hidden sources are not Compton-thick based on spectral analysis.

A correlation between excess variance and BAT luminosity is observed.

Spectral and flux variability insights enhance AGN population models.

Abstract

The fraction of Compton thick sources is one of the main uncertainties left in understanding the AGN population. The Swift Burst Alert Telescope (BAT) all-sky survey, for the first time gives us an unbiased sample of AGN for all but the most heavily absorbed sources (log NH > 25). Still, the BAT spectra (14 - 195 keV) are time-averaged over months of observations and therefore hard to compare with softer spectra from the Swift XRT or other missions. This makes it difficult to distinguish between Compton-thin and Compton-thick models. With Suzaku, we have obtained simultaneous hard (> 15 keV) and soft (0.3 - 10 keV) X-ray spectra for 5 Compton-thick candidate sources. We report on the spectra and a comparison with the BAT and earlier XMM observations. Based on both flux variability and spectral shape, we conclude that these hidden sources are not Compton-thick. We also report on a possible correlation between excess variance and Swift BAT luminosity from the 16 d binned light curves, which holds true for a sample of both absorbed (4 sources), unabsorbed (8 sources), and Compton thick (Circinus) AGN, but is weak in the 64 day binned BAT light curves.