46 research outputs found
Impact of neutron star oscillations on the accelerating electric field in the polar cap of pulsar: or could we see oscillations of the neutron star after the glitch in pulsar?
Pulsar "standard model", that considers a pulsar as a rotating magnetized
conducting sphere surrounded by plasma, is generalized to the case of
oscillating star. We developed an algorithm for calculation of the
Goldreich-Julian charge density for this case. We consider distortion of the
accelerating zone in the polar cap of pulsar by neutron star oscillations. It
is shown that for oscillation modes with high harmonic numbers (l,m) changes in
the Goldreich-Julian charge density caused by pulsations of neutron star could
lead to significant altering of an accelerating electric field in the polar cap
of pulsar. In the moderately optimistic scenario, that assumes excitation of
the neutron star oscillations by glitches, it could be possible to detect
altering of the pulsar radioemission due to modulation of the accelerating
field.Comment: 7 pages, 8 figures. Presented at the conference "Isolated Neutron
Stars: from the Interior to the Surface", London, April 24-28, 2006; to
appear in Astrophysics and Space Scienc
Plasma Magnetosphere Formation Around Oscillating Magnetized Neutron Stars
The notion of death line of rotating pulsars is applied to model of
oscillating neutron stars. It is shown that the magnetosphere of typical
non-rotating oscillating stars may not contain secondary plasma to support the
generation of radio emission in the region of open field lines of plasma
magnetosphere.Comment: Accepted for publication in Astrophysics & Space Scienc
The Geminga Fraction
Radio-quiet gamma-ray pulsars like Geminga may account for a number of the unidentified EGRET sources in the Galaxy. The number of Geminga-like pulsars is very sensitive to the geometry of both the gamma-ray and radio beams. Recent studies of the shape and polarization of pulse profiles of young radio pulsars have provided evidence that their radio emission originates in wide cone beams at altitudes that are a significant fraction (1 -10%) of their light cylinder radius. Such wide radio emission beams will be visible at a much larger range of observer angles than the narrow core components thought to originate at lower altitude. Using 3D geometrical modeling that includes relativistic effects from pulsar rotation, we study the visibility of such radio cone beams as well as that of the gamma-ray beams predicted by slot gap and outer gap models. From the results of this study one can obtain revised predictions for the fraction of Geminga-like, radio quiet pulsars present in the gamma-ray pulsar population
Particle Motion and Electromagnetic Fields of Rotating Compact Gravitating Objects with Gravitomagnetic Charge
The exact solution for the electromagnetic field occuring when the
Kerr-Taub-NUT compact object is immersed (i) in an originally uniform magnetic
field aligned along the axis of axial symmetry (ii) in dipolar magnetic field
generated by current loop has been investigated. Effective potential of motion
of charged test particle around Kerr-Taub-NUT gravitational source immersed in
magnetic field with different values of external magnetic field and NUT
parameter has been also investigated. In both cases presence of NUT parameter
and magnetic field shifts stable circular orbits in the direction of the
central gravitating object. Finally we find analytical solutions of Maxwell
equations in the external background spacetime of a slowly rotating magnetized
NUT star. The star is considered isolated and in vacuum, with monopolar
configuration model for the stellar magnetic field.Comment: 18 pages, 6 figures, new results in section 2 added, section 3 is
revised, 3 references are adde
Force-free magnetosphere of an aligned rotator with differential rotation of open magnetic field lines
Here we briefly report on results of self-consistent numerical modeling of a
differentially rotating force-free magnetosphere of an aligned rotator. We show
that differential rotation of the open field line zone is significant for
adjusting of the global structure of the magnetosphere to the current density
flowing through the polar cap cascades. We argue that for most pulsars
stationary cascades in the polar cap can not support stationary force-free
configurations of the magnetosphere.Comment: 5 pages, 4 figures. Presented at the conference "Isolated Neutron
Stars: from the Interior to the Surface", London, April 24-28, 2006; to
appear in Astrophysics and Space Science. Significantly revised version, a
mistake found by ourselfs in the numerical code was corrected, all presented
results are obtained with the correct version of the cod
The Contribution of Fermi Gamma-Ray Pulsars to the local Flux of Cosmic-Ray Electrons and Positrons
We analyze the contribution of gamma-ray pulsars from the first Fermi-Large
Area Telescope (LAT) catalogue to the local flux of cosmic-ray electrons and
positrons (e+e-). We present new distance estimates for all Fermi gamma-ray
pulsars, based on the measured gamma-ray flux and pulse shape. We then estimate
the contribution of gamma-ray pulsars to the local e+e- flux, in the context of
a simple model for the pulsar e+e- emission. We find that 10 of the Fermi
pulsars potentially contribute significantly to the measured e+e- flux in the
energy range between 100 GeV and 1 TeV. Of the 10 pulsars, 2 are old EGRET
gamma-ray pulsars, 2 pulsars were discovered with radio ephemerides, and 6 were
discovered with the Fermi pulsar blind-search campaign. We argue that known
radio pulsars fall in regions of parameter space where the e+e- contribution is
predicted to be typically much smaller than from those regions where Fermi-LAT
pulsars exist. However, comparing the Fermi gamma-ray flux sensitivity to the
regions of pulsar parameter space where a significant e+e- contribution is
predicted, we find that a few known radio pulsars that have not yet been
detected by Fermi can also significantly contribute to the local e+e- flux if
(i) they are closer than 2 kpc, and if (ii) they have a characteristic age on
the order of one mega-year.Comment: 21 pages, 6 figures, accepted for publication in JCA
Source population synthesis and the Galactic diffuse gamma-ray emission
Population synthesis is used to study the contribution from undetected
sources to the Galactic ridge emission measured by EGRET. Synthesized source
counts are compared with the 3rd EGRET catalogue at low and high latitudes. For
pulsar-like populations, 5-10% of the emission >100 MeV comes from sources
below the EGRET threshold. A steeper luminosity function can increase this to
20% without violating EGRET source statistics. Less luminous populations can
produce much higher values without being detected. Since the unresolved source
spectrum is different from the interstellar spectrum, it could provide an
explanation of the observed MeV and GeV excesses above the predictions, and we
give an explicit example of how this could work.Comment: Astrophysics and Space Science, in press. (Proceedings of Conference
'The multi-messenger approach to high-energy gamma-ray sources', Barcelona,
2006). Minor changes for accepted version, updated reference
Electromagnetic Fields and Charged Particle Motion Around Magnetized Wormholes
We perform a study to describe motion of charged particles under the
influence of electromagnetic and gravitational fields of a slowly rotating
wormhole with nonvanishing magnetic moment. We present analytic expression for
potentials of electromagnetic field for an axially symmetric slowly rotating
magnetized wormholes. While addressing important issues regarding the subject,
we compare our results of motion around black holes and wormholes in terms of
the ratio of radii of event horizons of a black hole and of the throat of a
wormhole. It is shown that both radial and circular motions of test bodies in
the vicinity of a magnetized wormhole could give rise to a peculiar
observational astrophysical phenomenon.Comment: 9 pages, 4 figures, 2 tables, accepted for publication in
Astrophysics & Space Scienc
Adjustment of the electric current in pulsar magnetospheres and origin of subpulse modulation
The subpulse modulation of pulsar radio emission goes to prove that the
plasma flow in the open field line tube breaks into isolated narrow streams. I
propose a model which attributes formation of streams to the process of the
electric current adjustment in the magnetosphere. A mismatch between the
magnetospheric current distribution and the current injected by the polar cap
accelerator gives rise to reverse plasma flows in the magnetosphere. The
reverse flow shields the electric field in the polar gap and thus shuts up the
plasma production process. I assume that a circulating system of streams is
formed such that the upward streams are produced in narrow gaps separated by
downward streams. The electric drift is small in this model because the
potential drop in narrow gaps is small. The gaps have to drift because by the
time a downward stream reaches the star surface and shields the electric field,
the corresponding gap has to shift. The transverse size of the streams is
determined by the condition that the potential drop in the gaps is sufficient
for the pair production. This yields the radius of the stream roughly 10% of
the polar cap radius, which makes it possible to fit in the observed
morphological features such as the "carousel" with 10-20 subbeams and the
system of the core - two nested cone beams.Comment: 8 pages, 1 figur
Constraints from CMB in the intermediate Brans-Dicke inflation
We study an intermediate inflationary stage in a Jordan-Brans-Dicke theory.
In this scenario we analyze the quantum fluctuations corresponding to adiabatic
and isocurvature modes. Our model is compared to that described by using the
intermediate model in Einstein general relativity theory. We assess the status
of this model in light of the seven-year WMAP data.Comment: 17 pages, 6 figure