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An electric field suffers a discontinuity at a surface charge. Similarly, a magnetic field is discontinuous at a surface current. The perpendicular component of a magnetic field is continuous across the interface of two magnetic mediums. In contrast, its parallel component, perpendicular to the current, is discontinuous by the amount equal to the product of the vacuum permeability and the surface current. Like the scalar potential in electrostatics, the vector potential is also continuous...
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The magnetic flux measures the number of magnetic field lines passing through a given surface area. The SI unit for magnetic flux is the weber (Wb). Magnetic flux is a scalar quantity. It depends on three factors: the strength of the magnetic field B, the area through which the field lines pass, and the relative orientation of the field with the surface area.
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Variable Nature of Magnetically-Driven Ultra-Fast Outflows.

Keigo Fukumura1, Demosthenes Kazanas2, Chris Shrader2,3

  • 1Department of Physics and Astronomy, James Madison University, Harrisonburg, VA 22807.

The Astrophysical Journal. Letters
|February 6, 2020
PubMed
Summary

Magnetohydrodynamic (MHD) accretion-disk winds explain ultra-fast outflows (UFOs) in the quasar PDS 456. Magnetic interactions, not just radiation pressure, drive these powerful outflows, matching observed X-ray properties.

Keywords:
(galaxies:) quasars: absorption linesaccretion, accretion disksgalaxies: individual (PDS 456)magnetohydrodynamics (MHD)methods: numerical

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Area of Science:

  • * Astrophysics
  • * High-energy astrophysics
  • * Plasma physics

Background:

  • * Active galactic nuclei (AGNs) can drive powerful ionized outflows, with ultra-fast outflows (UFOs) being a key phenomenon.
  • * The quasar PDS 456 at redshift z = 0.184 is a well-studied example exhibiting prominent UFOs.
  • * The precise acceleration mechanism for these UFOs remains a significant area of investigation.

Purpose of the Study:

  • * To model the variations in Fe K UFO properties of PDS 456 using magnetohydrodynamic (MHD) accretion-disk wind theory.
  • * To investigate the physical conditions of the UFO, including velocity, ionization, column density, and equivalent width (EW).
  • * To determine if magnetic interactions alone can drive UFOs and reproduce observed X-ray spectral correlations.

Main Methods:

  • * Application of a 2.5-dimensional MHD-driven wind model to X-ray spectra from XMM-Newton and NuSTAR observations (2013/2014).
  • * Photoionization calculations incorporating assumptions on X-ray luminosity dependence on accretion rate for near-Eddington states.
  • * Analysis of correlations between UFO velocity, EW, and X-ray luminosity.

Main Results:

  • * The MHD accretion-disk wind model successfully reproduces observed correlations of UFO velocity with X-ray luminosity.
  • * The model also replicates the anti-correlation between UFO EW and X-ray strength.
  • * The findings support the role of magnetic forces in driving UFOs, even in the absence of significant radiative pressure.

Conclusions:

  • * Magnetohydrodynamic (MHD) accretion-disk winds provide a viable mechanism for driving ultra-fast outflows (UFOs) in AGNs like PDS 456.
  • * Magnetic interaction is demonstrated as a primary driver for UFOs, capable of explaining observed spectral properties and correlations.
  • * This study highlights magnetic acceleration as an extreme but effective process for generating powerful outflows in quasars.