## Abstract

We solve for the time-dependent dynamics of axisymmetric, general relativistic magnetohydrodynamic winds from rotating neutron stars. The mass-loss rate as a function of latitude is obtained self-consistently as a solution to the magnetohydrodynamics 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 σ_{0}), almost thermally driven winds to high magnetization (high σ_{0}), relativistic Poynting-flux-dominated outflows ( with , where ω is the rotation rate, Φ is the open magnetic flux, and is the mass flux). We compute the angular momentum and rotational energy-loss rates as a function of σ_{0} and compare with analytic expectations from the classical theory of pulsars and magnetized stellar winds. In the case of the monopole, our high-σ_{0} 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 σ_{0} 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= cylindrical radius), as has previously been assumed in most estimates and force-free calculations. Instead, although the Alfvén radius at intermediate latitudes quickly approaches R_{L} as σ_{0} exceeds unity, r_{Y} remains significantly less than R_{L}. In addition, r_{Y} is a weak function of σ_{0}, suggesting that high magnetizations may be required to quantitatively approach the force-free magnetospheric structure, with . Because , our calculated spindown rates thus exceed the classic 'vacuum dipole' rate: equivalently, for a given spindown rate, the corresponding dipole field is smaller than traditionally inferred. In addition, our results suggest a braking index generically less than 3. We discuss the implications of our results for models of rotation-powered pulsars and magnetars, both in their observed states and in their hypothesized rapidly rotating initial states.

Original language | English (US) |
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Pages (from-to) | 1717-1734 |

Number of pages | 18 |

Journal | Monthly Notices of the Royal Astronomical Society |

Volume | 368 |

Issue number | 4 |

DOIs | |

State | Published - Jun 2006 |

Externally published | Yes |

## All Science Journal Classification (ASJC) codes

- Astronomy and Astrophysics
- Space and Planetary Science

## Keywords

- MHD
- Methods: numerical
- Relativity
- Stars: neutron
- Stars: winds, outflows