X-Ray Radiative Transfer Calculation Based on a Physics-based Model of the Sub-parsec-scale Gases around an Active Galactic Nucleus and Its Application to NGC 3783

TL;DR

This study models X-ray radiative transfer in the gas around an active galactic nucleus, explaining observed iron absorption lines and emission features through a physics-based simulation of sub-parsec-scale outflows.

Contribution

It introduces a comprehensive radiative transfer model combining hydrodynamics and photoionization calculations to explain X-ray spectral features in AGNs.

Findings

Absorption lines of He-like and H-like iron are produced at specific inclination angles.

The model reproduces observed iron absorption lines in NGC 3783.

Emission lines from various iron states are broadened by Keplerian rotation.

Abstract

Although the X-ray spectra of Seyfert 1 galaxies exhibit absorption lines of He-like iron and H-like iron at blue-shifted velocities of approximately $500 \ \mathrm{km} \ \mathrm{s}^{-1}$, the physical origin of these absorption lines remains uncertain. In this study, we performed X-ray radiative transfer based on the sub-parsec-scale thermally driven outflows. The initial step involved calculating the photoionization equilibrium using the Cloudy code, which is based on three-dimensional radiative hydrodynamic simulations. Subsequently, X-ray radiative transfer was performed using the Monte Carlo simulation for astrophysics and cosmology code. Our findings indicate that when the angle of inclination ranges from $55 \ \mathrm{degrees}$ to $65 \ \mathrm{degrees}$, the transmitted component of the X-ray spectrum displays absorption lines of He-like and H-like iron, exhibiting a blue shift of approximately $500 \ \mathrm{km} \ \mathrm{s}^{-1}$. The results suggest that the absorption lines are generated by a photoionized gas within $0.005 \ \mathrm{pc}$. Additionally, the results indicate that the scattered component of the X-ray spectrum exhibits emission lines originating from neutral iron fluorescence, He-like iron, and H-like iron. The emission lines are broadened by approximately $7000 \ \mathrm{km} \ \mathrm{s}^{-1}$ due to the Keplerian rotation. Furthermore, the model reproduced the H-like iron and H-like iron absorption lines in NGC 3783 observed by the Chandra High Energy Transmission Grating.