1 / 19

Theory of quasi-spherical accretion in X–ray pulsars

Theory of quasi-spherical accretion in X–ray pulsars. Shakura et al. Reporter: Zhang Zhen 11.11.28. A theoretical model for quasi-spherical subsonic accretion onto slowly rotating magnetized neutron stars Quasi-spherical shell Convective motions. Outlines. Introduction

Download Presentation

Theory of quasi-spherical accretion in X–ray pulsars

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Theory of quasi-spherical accretion in X–ray pulsars Shakura et al. Reporter: Zhang Zhen 11.11.28

  2. A theoretical model for quasi-spherical subsonic accretion onto slowly rotating magnetized neutron stars • Quasi-spherical shell • Convective motions

  3. Outlines • Introduction • Quasi-spherical accretion • Spin-up/spin-down transitions • Specific X-ray pulsars

  4. INTRODUCTION • Disk accretion • Wind accretion • Spin-up: be proportional to Fryxell & Taam (1988), Ruffert (1997), Ruffert (1999), etc Eccentricity & inhomogeneous • Spin-down: even more uncertain

  5. INTRODUCTION • Different ways for wind accreted on to NS • Burnard et al. (1983). • X-ray flux  cools down & freely falls down • Supersonic a shock above the magnetosphere • Davies & Pringle (1981) • X-ray flux weak to some extend • the radial velocity of the plasma is subsonic, • A hot quasi-static shell forms around the magnetosphere.

  6. QUASI-SPHERICAL ACCRETION • Aim: • Twoequations: The structure of the shell Hydrostatic equilibrium equation zeroth approximation

  7. QUASI-SPHERICAL ACCRETION • First approximation: the entropy distribution in the shell is constant • The Alfven surface

  8. QUASI-SPHERICAL ACCRETION • Prandtl law and isotropic turbulence • ω∗ > ωm: transfer of angular momentum from the magnetosphere to the shell • ω∗ < ωm: from the shell to the magnetosphere if • ω∗: angular velocity of NS

  9. QUASI-SPHERICAL ACCRETION • Strong coupling • Propeller / Equilibrium state • Moderate coupling • the plasma can enter the magnetosphere • instabilities on a timescale shorter than that needed for the toroidal field to grow to the value of the poloidal field

  10. The case of strong coupling • The turbulent magnetic field diffusion coefficient η Lovelace et al. 1995 • Energy: from the rotation of a magnetospheric surface to turbulence • ~ kinematic turbulent viscosity

  11. The case of strong coupling • RA > Rc, matter does not fall onto the neutron star, there are no accretion-generated X-rays from the neutron star, the shell rapidly cools down and shrinks and the standard Illarionov and Sunyaev propeller (1975) • Equilibrium state • RA > Rc

  12. The case of moderate coupling • Rayleigh-Taylor instability

  13. Spin-up/spin-down transitions

  14. Specific X-ray pulsars • GX 301-2 Doroshenko et al. 2010

  15. Vela X-1

  16. Reference • Arxiv: 1110.3701v1 • Arxiv: 1111.1382v1

  17. 没讲清的问题 • The plasma enters the magnetosphere of the slowly rotating neutron star due to the interchange instability.

  18. Thanks

More Related