A New Two-Fluid Radiation-Hydrodynamical Model for X-ray Pulsar Accretion Columns

Abstract

Previous research centered on the hydrodynamics in X-ray pulsar accretion columns has largely focused on the single-fluid model, in which the super-Eddington luminosity inside the column decelerates the flow to rest at the stellar surface. This type of model has been relatively successful in describing the overall properties of the accretion flows, but it does not account for the possible dynamical effect of the gas pressure. On the other hand, the most successful radiative transport models for pulsars generally do not include a rigorous treatment of the dynamical structure of the column, instead assuming an ad hoc velocity profile. In this paper, we explore the structure of X-ray pulsar accretion columns using a new, self-consistent, "two-fluid" model, which incorporates the dynamical effect of the gas and radiation pressure, the dipole variation of the magnetic field, the thermodynamic effect of all of the relevant coupling and cooling processes, and a rigorous set of physical boundary conditions. The model has six free parameters, which we vary in order to approximately fit the phase-averaged spectra in Her X-1, Cen X-3, and LMC X-4. In this paper, we focus on the dynamical results, which shed new light on the surface magnetic field strength, the inclination of the magnetic field axis relative to the rotation axis, the relative importance of gas and radiation pressure, and the radial variation of the ion, electron, and inverse-Compton temperatures. The results obtained for the X-ray spectra are presented in a separate paper.

arXiv commentAccepted for Publication in the Astrophysical Journal

References in corpus (22)

• Thermal and Bulk Comptonization in Accretion-Powered X-Ray Pulsars
• Spectral Formation in Accreting X-Ray Pulsars: Bimodal Variation of the Cyclotron Energy with Luminosity
• Three-dimensional Simulations of Disk Accretion to an Inclined Dipole: I. Magnetospheric Flow at Different Theta
• Discovery of a flux-related change of the cyclotron line energy in Her X-1
• Magnetically Driven Warping, Precession and Resonances in Accretion Disks
• A model for cyclotron resonance scattering features
• Analytical Hot Spot Shapes and Magnetospheric Radius from 3D Simulations of Magnetospheric Accretion
• Orbital Decay in LMC X-4
• The 0.1-100 keV Spectrum of LMC X-4 in the High State: Evidence for a High Energy Cyclotron Absorption Line
• Long-term change in the cyclotron line energy in Hercules X-1
• Burial of the polar magnetic field of an accreting neutron star. II. Hydromagnetic stability of axisymmetric equilibria
• Exact Expressions for the Critical Mach Numbers in the Two-Fluid Model of Cosmic-Ray Modified Shocks
• The NuSTAR X-ray Spectrum of Hercules X-1: A Radiation-Dominated Radiative Shock
• A radiation-hydrodynamic model of accretion columns for ultra-luminous X-ray pulsars
• Warping and Precession of Accretion Disks Around Magnetic Stars: Nonlinear Evolution
• MHD instabilities in accretion mounds - II. 3D simulations
• Pulse phase and precession phase resolved spectroscopy of Her X-1: studying a representative Main-On with RXTE
• Dynamical and Radiative Properties of X-ray Pulsar Accretion Columns: Phase-Averaged Spectra
• Quasiperiodic oscillations in Cen X-3 and the long term intensity variations
• Formation of phase lags at the cyclotron energies in the pulse profiles of magnetized, accreting neutron stars
• Accretion in dipole magnetic fields: flow structure and X-ray emission of accreting white dwarfs
• Hot Outflowing Gas from the X-ray Binary Hercules X-1

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• The 2019 super-Eddington outburst of RX J0209.6-7427: Detection of pulsations and constraints on the magnetic field strength
• M51 ULX-7: super-orbital periodicity and constraints on the neutron star magnetic field
• The X-ray polarimetry view of the accreting pulsar Cen X-3
• Revisiting the archetypical wind accretor Vela X-1 in depth -- A case study of a well-known X-ray binary and the limits of our knowledge
• NGC 300 ULX1: A test case for accretion torque theory
• Dynamical and Radiative Properties of X-ray Pulsar Accretion Columns: Phase-Averaged Spectra
• Investigating ULX accretion flows and cyclotron resonance in NGC 300 ULX1
• Radiative Relativistic Magnetohydrodynamic Simulations of Neutron Star Column Accretion in Cartesian Geometry
• Polarisation of Accreting X-ray Pulsars. II. Hercules X-1
• Dynamics of Neutron Star Accretion Columns in Split-Monopole Magnetic Fields
• A Bayesian approach for torque modelling of BeXRB pulsars with application to super-Eddington accretors
• Pulsed fraction of super-critical column accretion flows onto neutron stars: modeling of ultraluminous X-ray pulsars
• Simulating the shock dynamics of a neutron star accretion column
• Three-dimensional modelling of accretion columns: spatial asymmetry and self-consistent simulations
• Radiative MHD Simulations of Photon Bubbles in Radiation-Supported Magnetized Atmospheres of Neutron Stars with Isotropic Thomson Scattering
• Vacuum polarization alters the spectra of accreting X-ray pulsars
• Two-temperature accretion flows around strongly magnetized stars and their spectral analysis
• Hydrodynamical simulation of the structure of the X-ray pulsar accretion channel: accounting for resonant scattering
• Flux variability of the "10 keV feature" of 4U 0115+63