Tackling the soft X-ray excess in AGN with variability studies

TL;DR

This study investigates the origin of the soft X-ray excess in AGN by analyzing its variability over time, using multi-epoch spectral fitting, and finds it likely arises from thermal Comptonization based on observations of Mrk 841.

Contribution

It introduces a variability-based approach to determine the origin of the soft X-ray excess in AGN, demonstrating its effectiveness with detailed analysis of Mrk 841.

Findings

Soft X-ray excess varies significantly over years.

Variability timescale is constrained to a few days.

Thermal Comptonization best explains the soft excess variability.

Abstract

The origin of the soft X-ray excess in AGN has been a mystery ever since its discovery. We present how the time variability of this spectral component can point towards its origin. Using the powerful technique of multi-epoch fitting, we study how the soft excess in a given object depends on other parameters of the continuum and the accretion disk possibly hinting at its nature. As an example, we present results from this technique applied to the Seyfert galaxy Mrk 841. We study all (3) XMM and some of the Suzaku pointings available and find that the source displays an impressive variability in the soft X-ray band on the timescale of years. We study several common soft excess models and their ability to physically consistently explain this spectral variability. Mrk 841 is found to show a distinct variability pattern that can be best explained by the soft excess originating mostly from a thermal Comptonization component. The variability timescale can be constrained to be on the order of a few days.