Tell-Tale Spectral Signatures of MHD-driven Ultra-Fast Outflows in AGNs

TL;DR

This paper investigates spectral signatures of magnetohydrodynamic-driven ultra-fast outflows in active galactic nuclei, revealing characteristic asymmetric absorption lines that can serve as diagnostics for wind properties and driving mechanisms.

Contribution

It introduces a systematic analysis of MHD-driven UFO spectral features across key parameters and demonstrates their detectability with upcoming X-ray instruments.

Findings

MHD-driven UFOs produce asymmetric blue-tail absorption lines.

Spectral signatures depend on key wind parameters and viewing angles.

Upcoming X-ray missions can detect these tell-tale spectral features.

Abstract

We aim to explore spectral signatures of the predicted multi-ion UFOs in the broadband X-ray spectra of active galactic nuclei (AGNs) by exploiting an accretion disk wind model in the context of a simple magnetohydrodynamic (MHD) framework. We are focused primarily on examining the spectral dependences on a number of key properties; (1) ionizing luminosity ratio $\lambda_{\rm ion}$, (2) line-of-sight wind density slope $p$, (3) optical/UV-to-X-ray strength $\alpha_{\rm OX}$, (4) inclination $\theta$, (5) X-ray photon index $\Gamma$ and (6) wind density factor $f_D$. With an emphasis on radio-quiet Seyferts in sub-Eddington regime, multi-ion UFO spectra are systematically calculated as a function of these parameters to show that MHD-driven UFOs imprint a unique asymmetric absorption line profile with a pronounced blue tail structure on average. Such a characteristic line signature is generic to the simplified MHD disk-wind models presented in this work due to their specific kinematics and density structure. The properties of these absorption line profiles could be utilized as a diagnostics to distinguish between different wind driving mechanisms or even the specific values of a given MHD wind parameters. We also present high fidelity microcalorimeter simulations in anticipation of the upcoming {\it XRISM}/Resolve and {\it Athena}/X-IFU instruments to demonstrate that such a "tell-tale" sign may be immune to a spectral contamination by the presence of additional warm absorbers and partially covering gas.