---
author:
- 'J.M Ram[í]{}rez-Velasquez and Javier Garc[í]{}a'
title: 'X-ray outflows of active galactic nuclei warm absorbers: A 900 ks Chandra simulated spectrum'
---

Introduction
============

In active galactic nuclei (AGNs), photoionization has been recognized as the main mechanism for the formation of Ultraviolet (UV) and X-ray lines ([@bahcall1969a]). If the photo-ionized plasma reaches a stable state for their ion populations, they are said to be in photo-ionization equilibrium (PIE). Under the assumption of PIE, one of the principal parameters describing the physical condition of the plasma is the ionization parameter $\xi$: $$\xi(r)=\frac{L}{n_H(r)r^2},
\label{xi11}$$ where $L$ is the ionizing luminosity of the primary source, $n_H(r)$ is the gas density, and $r$ is the distance from the ionizing source to the interacting shell/slab of plasma. Therefore, spectral fitting to the observational data in the X-ray band of a given source combined with a measurement of its luminosity $L$ provide constrains on the degenerated quantity $n_H(r)r^2$. Moreover, in order to have an estimate of the spatial location of the gas absorbing/emitting photons from the primary underlying source, an independent determination of the gas density $n_H(r)$ is required.

Curve of growth (COG) ([@spitzer1998a]) is a useful tool to gather information from astrophysical spectra, 