2025/10/22 by Fukumura, Keigo, Ogawa, Shoji, Tanimoto, Atsushi +6
#FOS: Physical sciences #High Energy Astrophysical Phenomena (astro-ph.HE)
paper · doi:10.48550/arxiv.2510.19539
Powerful ionized accretion disk winds are often observed during episodic outbursts in Galactic black hole transients. Among those X-ray absorbers, \fexxvi doublet structure (Lyα1+Lyα2 with ∼ 20eV apart) has a unique potential to better probe the underlying physical nature of the wind; i.e. density and kinematics. We demonstrate, based on a physically-motivated magnetic disk wind scenario of a stratified structure in density and velocity, that the doublet line profile can be effectively utilized as a diagnostics to measure wind density and associated velocity dispersion (due to thermal turbulence and/or dynamical shear motion in winds). Our simulated doublet spectra with post-process radiative transfer calculations indicate that the profile can be (1) broad with a single peak for higher velocity dispersion (\gsim 5,000 km~s-1), (2) a standard shape with 1:2 canonical flux ratio for moderate dispersion (∼ 1,000-5,000 km~s-1) or (3) double-peaked with its flux ratio approaching 1:1 for lower velocity dispersion (\lsim 1,000 km~s-1) in optically-thin regime, allowing various line shape. Such a diversity in doublet profile is indeed unambiguously seen in recent observations with XRISM/Resolve at microcalorimeter resolution. We show that some implications inferred from the model will help constrain the local wind physics where \fexxvi is predominantly produced in a large-scale, stratified wind.