36,990 research outputs found
Velocity-dependent energy gaps and dynamics of superfluid neutron stars
We show that suppression of the baryon energy gaps, caused by the relative
motion of superfluid and normal liquid components, can substantially influence
dynamical properties and evolution of neutron stars. This effect has been
previously ignored in the neutron-star literature.Comment: 6 pages, 5 figures, accepted by MNRAS Let
Precession of the Isolated Neutron Star PSR B1828-11
Stairs, Lyne & Shemar have found that arrival time residuals from PSR
B1828-11 vary periodically with a period of 500 days. This behavior can be
accounted for by precession of the radiopulsar, an interpretation that is
reinforced by the detection of variations in its pulse profile on the same
timescale. Here, we model the period residuals from PSR B1828-11 in terms of
precession of a triaxial rigid body. We include two contributions to the
residuals: (i) the geometric effect, which arises because the times at which
the pulsar emission beam points toward the observer varies with precession
phase; (ii) the spindown contribution, which arises from any dependence of the
spindown torque acting on the pulsar on the angle between its spin and magnetic
axes. We use the data to probe numerous properties of the pulsar, most notably
its shape, and the dependence of its spindown torque on the angle between its
spin and magnetic axes, for which we assume a sum of a spin-aligned component
(with a weight 1-a) and a dipolar component perpendicular to the magnetic beam
axis (weight a), rather than the vacuum dipole torque (a=1). We find that a
variety of shapes are consistent with the residuals, with a slight statistical
preference for a prolate star. Moreover, a range of torque possibilities fit
the data equally well, with no strong preference for the vacuum model. In the
case of a prolate star we find evidence for an angle-dependent spindown torque.
Our results show that the combination of geometrical and spin-down effects
associated with precession can account for the principal features of PSR
B1828-11's timing behavior, without fine tuning of the parameters.Comment: 22 pages, 14 figures, submitted to MNRAS; added references, corrected
typo
Constraining the Origin of Magnetar Flares
Sudden relaxation of the magnetic field in the core of a magnetar produces
mechanical energy primarily in the form of shear waves which propagate to the
surface and enter the magnetosphere as relativistic Alfv\'en waves. Due to a
strong impedance mismatch, shear waves excited in the star suffer many
reflections before exiting the star. If mechanical energy is deposited in the
core and is converted {\em directly} to radiation upon propagation to the
surface, the rise time of the emission is at least seconds to minutes, and
probably minutes to hours for a realistic magnetic field geometry, at odds with
observed rise times of \lap 10 ms for both and giant flares. Mechanisms for
both small and giant flares that rely on the sudden relaxation of the magnetic
field of the core are rendered unviable by the impedance mismatch, requiring
the energy that drives these events to be stored in the magnetosphere just
before the flare. ends, unless the waves are quickly damped.Comment: Final version in Monthly Notices of the Royal Astronomical Society.
13 pages, 5 figure
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