Transient particle acceleration in strongly magnetized neutron stars. II. Effects due to a dipole field geometry

Marco Fatuzzo, Fulvio Melia

Research output: Contribution to journalArticle

2 Scopus citations

Abstract

Sheared Alfvén waves generated by nonradial crustal disturbances above the polar cap of a stronngly magnetized neutron star (B ≲ 1012 gauss) induce an electric field component parallel to B. Earlier calculations assuming a uniform magnetic field showed that this mechanism could successfully accelerate particles to Lorentz factors γ ∼ (50 cm) m, where m (∼2-3 cm-1) characterizes the degree of shearing. However, magnetic field gradients in a realistic dipole field geometry cannot be ignored. Our goal here is to determine the manner in which the strong radial dependence of B affects the propagation of these sheared Alfvén waves, and whether this magnetohydrodynamic process is still an effective particle accelerator. By comparison to the field gradients, the field-line curvature is small within a stellar radius of the polar cap, and we therefore use an approximate form of the dipole field that ignores the component perpendicular to the z-axis. We find that although the general field equation is quite complicated, a simple wavelike solution can still be obtained under the conditions of interest (i.e., B ≲ 1012 G, and a particle number density ne ≲ 1026 cm-3) for which the Alfvén phase velocity → c and ne decouples from the wave equation. Our results may be applicable to γ-ray burst sources.

Original languageEnglish (US)
Pages (from-to)570-575
Number of pages6
JournalAstrophysical Journal
Volume382
Issue number2
DOIs
StatePublished - Dec 1 1991

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Keywords

  • Gamma rays: bursts
  • Gamma rays: general
  • Magnetic fields
  • Particle acceleration
  • Pulsars
  • Stars : neutron

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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