Emission and Absorption Features of Magnetically Driven Disk Winds in Black Hole X-Ray Binaries

TL;DR

This study models magnetically driven accretion disk winds in black hole X-ray binaries using 3D radiative transfer simulations, revealing how wind geometry affects observed spectral features and explaining observed absorption and emission line profiles.

Contribution

It introduces a comprehensive MHD wind model combined with Monte Carlo radiative transfer to explain spectral features in BH XRBs, highlighting the impact of viewing angle.

Findings

High polar angle systems show prominent multi-ion absorption lines.

Asymmetric line profiles and P-Cygni features are reproduced in simulations.

Dense winds at high angles are unlikely to be saturated due to scattering effects.

Abstract

We investigate accretion disk winds commonly observed in galactic black hole (BH) X-ray binaries (XRB), which manifest as blueshifted absorption features in X-ray spectra. We model these winds as ideal magnetohydrodynamic outflows of hot plasma driven by global magnetic fields threading the accretion disk around the BH. Using Monte Carlo simulations with MONACO, we solve three-dimensional radiative transfer equations to determine the large-scale ionization structure that produces the observed ionic column densities. Focusing on the high/soft state of the BH XRB, where disk emission provides the dominant source of ionizing X-rays, we calculated synthetic spectra showing resonance absorption and scattered emission from ions in various charge states. Our results demonstrate that systems viewed at high polar angles exhibit prominent multi-ion absorption lines with asymmetric profiles, accompanied by P-Cygni-like emission features that partially reproduce the characteristics seen in the observed spectra. This further implies that even a dense disk wind with a high polar angle is unlikely to be saturated due to effective scattering.