Magnetic fields in axisymmetric neutron stars

Abstract

We derive general equations for axisymmetric Newtonian MHD and use these as the basis of a code for calculating equilibrium configurations of rotating magnetised neutron stars in a stationary state. We investigate the field configurations that result from our formalism, which include purely poloidal, purely toroidal and mixed fields. For the mixed-field formalism the toroidal component appears to be bounded at less than 7%. We calculate distortions induced both by magnetic fields and by rotation. From our non-linear work we are able to look at the realm of validity of perturbative work: we find for our results that perturbative-regime formulae for magnetic distortions agree to within 10% of the nonlinear results if the ellipticity is less than 0.15 or the average field strength is less than $10^{17}$ G. We also consider how magnetised equilibrium structures vary for different polytropic indices.Comment: 19 pages, 11 figures; typos removed, one paragraph of Discussion rewritte

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“…Neutron star surface cooling observations , deformation induced oscillations (Lander & Jones 2009) and precession (Wasserman 2003), quasi-periodic oscillations (Gabler et al 2013) and magnetar bursts (Perna & Pons 2011) provide indirect restrictions on the toroidal field strength and location. As shown in this paper for the first time, glitch observations in turn give a novel opportunity to infer toroidal field characteristics pertaining to superfluid/superconducting outer core, within the vortex creep model.…”

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Gravitational Waves from Color-Magnetic “Mountains” in Neutron Stars

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