Tell-tale Spectral Signatures of MHD-driven Ultrafast Outflows in AGNs

Abstract

We aim to explore spectral signatures of the predicted multi-ion ultrafast outflows (UFOs) in the broadband X-ray spectra of active galactic nuclei 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 λ ion, (2) line-of-sight wind density slope p, (3) optical/UV-to-X-ray strength α OX, (4) inclination θ, (5) X-ray photon index Γ, and (6) wind density factor f D . With an emphasis on radio-quiet Seyferts in the 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 given MHD wind parameters. We also present high-fidelity microcalorimeter simulations in anticipation of the upcoming XRISM/Resolve and 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.