Olindo Zanotti, Viktoriya Morozova, Bobomurat Ahmedov
We have revisited the issue of particle acceleration in the polar cap region
of a neutron star by taking into account both general relativistic effects and
the presence of toroidal oscillations at the star surface. In particular, we
address the question of whether toroidal oscillations of the star surface can
affect the acceleration properties in the polar cap. We have solved numerically
the relativistic electrodynamics equations in the stationary regime, focusing
on the computation of the Lorentz factor of a space-charge-limited electron
flow accelerated in the polar cap region of a rotating as well as oscillating
pulsar. To this extent, the correct expression for the general relativistic
Goldreich-Julian charge density in the presence of toroidal oscillations has
been adopted. Depending on the ratio between the actual charge density of the
pulsar magnetosphere and the Goldreich-Julian charge density, two different
regimes of the Lorentz factor of the particle flow are found. Namely an
oscillatory regime, which is produced for sub-GJ current density
configurations, and which does not produce an efficient acceleration, and a
true accelerating regime, which is produced for super-GJ current density
configurations. We have found that star oscillations may become responsible of
a significant asymmetry of the pulse profile, which will depend on the
orientation of the oscillations with respect to the pulsar magnetic field. In
particular, significant enhancements of the Lorentz factor are produced by star
oscillations in the super-GJ current density regime.
View original:
http://arxiv.org/abs/1111.0563
No comments:
Post a Comment