248 research outputs found
Differentially rotating force-free magnetosphere of an aligned rotator: analytical solutions in split-monopole approximation
In this paper we consider stationary force-free magnetosphere of an aligned
rotator when plasma in the open field line region rotates differentially due to
presence of a zone with the accelerating electric field in the polar cap of
pulsar. We study the impact of differential rotation on the current density
distribution in the magnetosphere. Using split-monopole approximation we obtain
analytical expressions for physical parameters of differentially rotating
magnetosphere. We find the range of admitted current density distributions
under the requirement that the potential drop in the polar cap is less than the
vacuum potential drop. We show that the current density distribution could
deviate significantly from the ``classical'' Michel distribution and could be
made almost constant over the polar cap even when the potential drop in the
accelerating zone is of the order of 10 per cents of the vacuum potential drop.
We argue that differential rotation of the open magnetic field lines could play
an important role in adjusting between the magnetosphere and the polar cap
cascade zone and could affect the value of pulsar breaking index.Comment: 15 pages, 15 figures; accepted for publication in MNRA
A model for nulling and mode changing in pulsars
We propose that in some pulsars the magnetosphere has different states with
different geometries or/and different distributions of currents, it
occasionally switches between them. These states have different spindown rates
and emission beams, in some of the states no radioemission is produced at all.
Switching into a different state manifests as a mode change when we see
different parts of the emission beam or the beams in different states have
significantly different geometries, it manifests as nulling when we either miss
the new beam or no radioemission is generated in the new state. We show that
modest variations in the beam shape can be accompanied by large variations in
the pulsar spindown rate W - the dependence of W on the opening angle of the
emission beam can be as strong as W\propto\alpha^4. We speculate about
physical mechanisms which may cause reconfiguration of the magnetosphere.Comment: 5 pages, 1 figure; MNRAS, in pres
Optical counterparts of cosmological GRBs due to heating of ISM in the parent galaxy
We investigated influence of cosmological GRB on the surrounding interstellar
medium. It was shown that \gamma-radiation from the burst heats interstellar
gas to the temperatures > 10^4 K up to the distance \sim 10 pc. For high
density ISM optical and UV radiation of the heated gas can be observed on the
Eath several years as a GRB`s counterpartComment: 2 pages, 1 figure; presented at the Rome Conference on Gamma Ray
Bursts in the Afterglow Ag
On the nature of QPO in the tail of SGR giant flares
A model is presented for the quasiperiodic component of magnetar emission
during the tail phase of giant flares. The model invokes modulation of the
particle number density in the magnetosphere. The magnetospheric currents are
modulated by torsional motion of the surface and we calculate that the
amplitude of neutron star surface oscillation should be ~1% of the NS radius in
order to produce the observed features in the power spectrum. Using an
axisymmetric analytical model for structure of the magnetosphere of an
oscillating NS, we calculate the angular distribution of the optical depth to
the resonant Compton scattering. The anisotropy of the optical depth may be why
QPO are observed only at particular rotational phases.Comment: 7 pages, 4 figures, emulateapj styl
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