Long-Term X-ray Spectral Variability of Seyfert Galaxies with Swift

TL;DR

This study analyzes long-term X-ray spectral variability in Seyfert galaxies using Swift data, revealing flux-dependent spectral changes and the necessity of models involving intrinsic luminosity changes and variable absorption.

Contribution

It introduces a comprehensive analysis of long-term X-ray spectral variability in Seyfert galaxies, highlighting the importance of combined intrinsic and absorption variability models.

Findings

Spectral softening at high fluxes

Spectral softening at very low fluxes

Variable absorption and intrinsic luminosity are both needed to explain the data

Abstract

We present analysis of the long-term X-ray spectral variability of Seyfert galaxies as observed by Swift, which provides well-sampled observations over a much larger flux range and a much longer timescale than any other X-ray observatory. We examine long-term variability of three AGN: NGC 1365 (see Connolly et al. 2014), Mkn 335 and NGC 5548. At high fluxes, the 0.5-10 keV spectra soften with increasing flux, as seen previously within the 2-10 keV band. However, at very low fluxes the sources also become very soft. We have fitted a number of models to the data and find that both intrinsic luminosity variability and variable absorption are required to explain the observations. In some systems, e.g. NGC 1365, the best explanation is a two-component wind model in which one component represents direct emission absorbed by a disc wind wind, with the absorbing column inversely proportional to the intrinsic luminosity, and the second component represents unabsorbed emission reflected from the wind. In other AGN the situation is more complex.