Implications of Non-equatorial Relativistic Accretion Flows for Ultra-Fast Inflows in AGNs

TL;DR

This paper models non-equatorial relativistic accretion flows in AGNs as a potential origin of ultra-fast inflows, using general relativistic hydrodynamics to simulate their spectral signatures and compare with observations.

Contribution

It introduces a new model of off-equatorial relativistic accretion flows guided by magnetic fields, explaining ultra-fast inflows observed in AGNs.

Findings

GRHD flows can produce redshifted absorption signatures consistent with UFIs.

Accretion velocities near 0.1c can occur within 100 Schwarzschild radii.

Model matches observed column densities and ionization parameters.

Abstract

Motivated by a number of X-ray observations of active galactic nuclei (AGNs) that exhibit a potential signature of ultra-fast inflows (UFIs), we consider in this work a scenario that UFIs can be physically identified as weakly-magnetized hydrodynamic accretion flows that is guided and channeled by poloidal magnetic field into low-to-mid latitude above the equatorial disk. In the context of general relativistic hydrodynamics (GRHD) under a weak-field limit in Kerr spacetime, we present a set of preliminary results by numerically calculating the physical property of GRHD flows (e.g. kinematics and density distribution) in an effort to simulate redshifted absorption line spectra. Our model demonstrates that such GRHD accretion off the equatorial plane (i.e. $v \gsim 0.1c$ where $c$ is the speed of light in the vicinity of AGN closer than $\sim 100$ \sw radii) can manifest itself as UFIs in the form of redshifted absorption signature assuming the observed characteristics such as column density of $N_H \sim 10^{23}$ cm$^{-2}$ and ionization parameter of $\log (\xi \rm{[erg~cm~s^{-1}])} \sim 3$ as also seen in recent multi-epoch {\it NuSTAR} observations among other data.