Alpha Mastrano, Andrew Melatos
Recent calculations of the hydromagnetic deformation of a stratified,
non-barotropic neutron star are generalized to describe objects with
superconducting interiors, whose magnetic permeability \mu is much smaller than
the vacuum value \mu_0. It is found that the star remains oblate if the
poloidal magnetic field energy is \gtrsim 40% of total magnetic field energy,
that the toroidal field is confined to a torus which shrinks as \mu decreases,
and that the deformation is much larger (by a factor \sim \mu_0/\mu) than in a
non-superconducting object. The results are applied to the latest direct and
indirect upper limits on gravitational-wave emission from Laser Interferometer
Gravitational Wave Observatory (LIGO) and radio pulse timing (spin-down)
observations of 81 millisecond pulsars, to show how one can use these
observations to infer the internal field strength. It is found that the
indirect spin-down limits already imply astrophysically interesting constraints
on the poloidal-toroidal field ratio and diamagnetic shielding factor (by which
accretion reduces the observable external magnetic field, e.g. by burial).
These constraints will improve following gravitational-wave detections, with
implications for accretion-driven magnetic field evolution in recycled pulsars
and the hydromagnetic stability of these objects' interiors.
View original:
http://arxiv.org/abs/1112.1542
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