How to estimate the distance to the Warm Absorber in AGN from photoionized models

TL;DR

This paper introduces a method to estimate the distance to warm absorbers in AGN by using photoionization models that analyze absorption line characteristics influenced by the ionized gas and radiation components.

Contribution

The authors develop a set of constant total pressure photoionization models incorporating a double power-law continuum to determine the warm absorber's distance based on absorption line features.

Findings

Different absorption line characteristics depend on hydrogen number density.

Soft component dominance leads to free-free absorption heating.

Distance estimation is feasible from observed absorption lines.

Abstract

We present a method that allows us to estimate the distance from the continuum source located in the center of AGN to the highly ionized gas called warm absorber. We compute a set of constant total pressure photoionization models compatible with the warm absorber conditions, where a metal-rich gas is irradiated by a continuum in the form of a double power-law. The first power-law is hard up to 100 keV and represents a radiation from an X-ray source, while the second power-law extends downwards from several eVs and illustrates a radiation from an accretion disk. When the ionized continuum is dominated by the soft component, the warm absorber is heated by free-free absorption, instead of Comptonization, and the transmitted spectra show different absorption line characteristics for different values of the hydrogen number density at the cloud illuminated surface. This fact results in the possibility of deriving the number density at the cloud illuminated side from observations and hence the distance to the warm absorber.