Magnetically-Driven Accretion-Disk Winds and Ultra-Fast Outflows in PG1211+143

TL;DR

This study models magnetically-driven accretion disk winds in AGNs to explain ultra-fast outflows observed in X-ray spectra, demonstrating their physical plausibility and matching observed absorption features.

Contribution

The paper develops a stratified MHD wind model that reproduces observed X-ray absorption features in AGNs, linking magnetic driving mechanisms to ultra-fast outflows.

Findings

Absorber has ionization parameter log(ξ) ≈ 5-6.

Column density is about 10^{23} cm^{-2}.

Outflow velocity is approximately 0.1-0.2c.

Abstract

We present a study of X-ray ionization of magnetohydrodynamic (MHD) accretion-disk winds in an effort to constrain the physics underlying the highly-ionized ultra-fast outflows (UFOs) inferred by X-ray absorbers often detected in various sub-classes of Seyfert active galactic nuclei (AGNs). Our primary focus is to show that magnetically-driven outflows are indeed physically plausible candidates for the observed outflows accounting for the AGN absorption properties of the present X-ray spectroscopic observations. Employing a stratified MHD wind launched across the entire AGN accretion disk, we calculate its X-ray ionization and the ensuing X-ray absorption line spectra. Assuming an appropriate ionizing AGN spectrum, we apply our MHD winds to model the absorption features in an {\it XMM-Newton}/EPIC spectrum of the narrow-line Seyfert, \pg. We find, through identifying the detected features with Fe K$\alpha$ transitions, that the absorber has a characteristic ionization parameter of $\log (\xi_c [erg~cm~s$^{-1}$]) \simeq 5-6$ and a column density on the order of $N_H \simeq 10^{23}$ cm$^{-2}$, outflowing at a characteristic velocity of $v_c/c \simeq 0.1-0.2$ (where $c$ is the speed of light). The best-fit model favors its radial location at $r_c \simeq 200 R_o$ ($R_o$ is the black hole innermost stable circular orbit), with an inner wind truncation radius at $R_{\rm t} \simeq 30 R_o$. The overall K-shell feature in the data is suggested to be dominated by \fexxv\ with very little contribution from \fexxvi\ and weakly-ionized iron, which is in a good agreement with a series of earlier analysis of the UFOs in various AGNs including \pg.