paper

Relativistic MHD Winds from Rotating Neutron Stars

arXiv:astro-ph/0602475 · doi:10.1111/j.1365-2966.2006.10217.x

Abstract

We solve for the time-dependent dynamics of axisymmetric, general relativistic magnetohydrodynamic winds from rotating neutron stars. The mass loss rate is obtained self-consistently as a solution to the MHD equations, subject to a finite thermal pressure at the stellar surface. We consider both monopole and dipole magnetic field geometries and we explore the parameter regime extending from low magnetization (low-sigma_o), almost thermally-driven winds to high magnetization (high-sigma_o), relativistic Poynting-flux dominated outflows. We compute the angular momentum and rotational energy loss rates as a function of sigma_o and compare with analytic expectations from the classical theory of pulsars and magnetized stellar winds. In the case of the monopole, our high-sigma_o calculations asymptotically approach the analytic force-free limit. If we define the spindown rate in terms of the open magnetic flux, we similarly reproduce the spindown rate from recent force-free calculations of the aligned dipole. However, even for sigma_o as high as ~20, we find that the location of the Y-type point (r_Y), which specifies the radius of the last closed field line in the equatorial plane, is not the radius of the light cylinder R_L = c/omega (R = cylindrical radius), as has previously been assumed in most estimates and force-free calculations. Instead, although the Alfven radius at intermediate latitudes quickly approaches R_L as sigma_o exceeds unity, r_Y remains significantly less than R_L. Because r_Y < R_L, our calculated spindown rates thus exceed the classic ``vacuum dipole'' rate. We discussthe implications of our results for models of rotation-powered pulsars and magnetars, both in their observed states and in their hypothesized rapidly rotating initial state.

Accepted for publication in MNRAS. 19 pages, 21 figures

References in corpus (26)

Cited by in corpus (98)