656 research outputs found
Chaotic Motion of Relativistic Electrons Driven by Whistler Waves
Canonical equations governing an electron motion in electromagnetic field of the whistler mode waves propagating along the direction of an ambient magnetic field are derived. The physical processes on which the equations of motion are based .are identified. It is shown that relativistic electrons interacting with these fields demonstrate chaotic motion, which is accompanied by the particle stochastic heating and significant pitch angle diffusion. Evolution of distribution functions is described by the Fokker-Planck-Kolmogorov equations. It is shown that the whistler mode waves could provide a viable mechanism for stochastic energization of electrons with energies up to 50 MeV in the Jovian magnetosphere
Stochastic electron motion driven by space plasma waves
Stochastic motion of relativistic electrons under conditions of the nonlinear
resonance interaction of particles with space plasma waves is studied.
Particular attention is given to the problem of the stability and variability
of the Earth's radiation belts. It is found that the interaction between
whistler-mode waves and radiation-belt electrons is likely to involve the
same mechanism that is responsible for the dynamical balance between the
accelerating process and relativistic electron precipitation events. We have
also considered the efficiency of the mechanism of stochastic surfing
acceleration of cosmic electrons at the supernova remnant shock front, and
the accelerating process driven by a Langmuir wave packet in producing cosmic
ray electrons. The dynamics of cosmic electrons is formulated in terms of a
dissipative map involving the effect of synchrotron emission. We present
analytical and numerical methods for studying Hamiltonian chaos and
dissipative strange attractors, and for determining the heating extent and
energy spectra
Isotropization of Ultra-High Energy Cosmic Ray Arrival Directions by Radio Ghosts
The isotropy in the ultra high energy cosmic ray (UHECR) flux observed by
Yakutsk and AGASA experiments, is a very strong constraint to production and
propagation models alike. Most of the scenarios proposed in the literature
should produce a sizable anisotropy as either extragalactic luminous or dark
matter is normally associated with the invoked particle sources. We explore the
possibility that the magnetic fields in fossil cocoons of former radio galaxies
-- so called {\it radio ghosts} -- are able to scatter UHECR in the
intergalactic medium giving rise to the observed isotropy. We show, through
numerical simulations, under which conditions this process can be operative and
the magnitude of the effect. We further demonstrate, that if radio ghosts mix
with the ambient medium, they might be able to produce the observed magnetic
fields in clusters of galaxies. In the case of mixing, the UHECR isotropization
would be even stronger than in our conservative estimates.Comment: Astroparticle Physics (accepted)--30 pages, 13 figures--please,
contact GMT for higher quality figure
Magnetized cosmic walls
Nonlinear growth of one-dimensional density structures with a frozen-in
magnetic field is investigated in Newtonian cosmology. A mechanism of magnetic
field amplification is discussed. We discuss the relation between the initial
conditions for the velocity field and the basic time-scales determining the
growth of the magnetized structure.Comment: 7 pages, 3 figures included; A&A accepte
A Faraday Rotation Search for Magnetic Fields in Large Scale Structure
Faraday rotation of radio source polarization provides a measure of the
integrated magnetic field along the observational lines of sight. We compare a
new, large sample of Faraday rotation measures (RMs) of polarized extragalactic
sources with galaxy counts in Hercules and Perseus-Pisces, two nearby
superclusters. We find that the average of RMs in these two supercluster areas
are larger than in control areas in the same galactic latitude range. This is
the first RM detection of magnetic fields that pervade a supercluster volume,
in which case the fields are at least partially coherent over several
megaparsecs. Even the most conservative interpretation of our observations,
according to which Milky Way RM variations mimic the background supercluster
galaxy overdensities, puts constraints on the IGM magneto-ionic ``strength'' in
these two superclusters. We obtain an approximate typical upper limit on the
field strength of about 0.3 microGauss l/(500 kpc), when we combine our RM data
with fiducial estimates of electron density from the environments of giant
radio galaxies, and of the warm-hot intergalactic medium (WHIM).Comment: 8 pages, 3 figures, 1 table, to appear in the Astrophysical Journa
Dynamic Theory of Relativistic Electrons Stochastic Heating by Whistler Mode Waves with Application to the Earth Magnetosphere
In the Hamiltonian approach an electron motion in a coherent packet of the whistler mode waves propagating along the direction of an ambient magnetic field is studied. The physical processes by which these particles are accelerated to high energy are established. Equations governing a particle motion were transformed in to a closed pair of nonlinear difference equations. The solutions of these equations have shown there exists the energetic threshold below that the electron motion is regular, and when the initial energy is above the threshold an electron moves stochastically. Particle energy spectra and pitch angle electron scattering are described by the Fokker-Planck-Kolmogorov equations. Calculating the stochastic diffusion of electrons due to a spectrum of whistler modes is presented. The parametric dependence of the diffusion coefficients on the plasma particle density, magnitude of wave field, and the strength of magnetic field is studies. It is shown that significant pitch angle diffusion occurs for the Earth radiation belt electrons with energies from a few keV up to a few MeV
Gravitational waves and cosmic magnetism; a cosmological approach
We present the formalism for the covariant treatment of gravitational
radiation in a magnetized environment and discuss the implications of the field
for gravity waves in the cosmological context. Our geometrical approach brings
to the fore the tension properties of the magnetic force lines and reveals
their intricate interconnection to the spatial geometry of a magnetised
spacetime. We show how the generic anisotropy of the field can act as a source
of gravitational wave perturbations and how, depending on the spatial curvature
distortion, the magnetic tension can boost or suppress waves passing through a
magnetized region.Comment: Minor changes. References added. To appear in Class. Quantum Gra
Dynamical Systems Approach to Magnetised Cosmological Perturbations
Assuming a large-scale homogeneous magnetic field, we follow the covariant
and gauge-invariant approach used by Tsagas and Barrow to describe the
evolution of density and magnetic field inhomogeneities and curvature
perturbations in a matter-radiation universe. We use a two parameter
approximation scheme to linearize their exact non-linear general-relativistic
equations for magneto-hydrodynamic evolution. Using a two-fluid approach we set
up the governing equations as a fourth order autonomous dynamical system.
Analysis of the equilibrium points for the radiation dominated era lead to
solutions similar to the super-horizon modes found analytically by Tsagas and
Maartens. We find that a study of the dynamical system in the dust-dominated
era leads naturally to a magnetic critical length scale closely related to the
Jeans Length. Depending on the size of wavelengths relative to this scale,
these solutions show three distinct behaviours: large-scale stable growing
modes, intermediate decaying modes, and small-scale damped oscillatory
solutions.Comment: 15 pages RevTeX, 5 figures. Accepted for publication in Physical
Review
Dipolarization Fronts in the Jovian Magnetotail: Statistical Survey of Ion Intensity Variations Using Juno Observations
Energetic particle acceleration and energization in planetary magnetotails are often associated with dipolarization fronts characterized by a rapid increase of the meridional component of the magnetic field. Despite many studies of dipolarization events in Earth's magnetotail, Jupiter’s magnetotail provides an almost ideal environment to study high-energetic ion acceleration by dipolarization fronts because of its large spatial scales and plasma composition of heavy and light ions. In this study, we focus on the response of different high-energetic ion intensities (H, He, S, and O) to prominent magnetic dipolarization fronts inside the Jovian magnetotail. We investigate if ion energization and acceleration are present in the observations around the identified dipolarization fronts. Therefore, we present a statistical study of 87 dipolarization front signatures, which are identified in the magnetometer data of the Juno spacecraft from July 2016 to July 2021. For the ion intensity analysis, we use the energetic particle observations from the Jupiter Energetic Particle Detector Instrument. Our statistical study reveals that less than half of the identified events are accompanied by an increase of the ion intensities, while most of the other events show no significant change in the ion intensity dynamics. In about 40% of the events located in the dawn sector a significant decrease of the energy spectral index is detected indicating ion acceleration by the dipolarization fronts
A Magnetized Local Supercluster and the Origin of the Highest Energy Cosmic Rays
A sufficiently magnetized Local Supercluster can explain the spectrum and
angular distribution of ultra-high energy cosmic rays. We show that the
spectrum of extragalactic cosmic rays with energies below eV may
be due to the diffusive propagation in the Local Supercluster with fields of
Gauss. Above eV, cosmic rays propagate
in an almost rectilinear way which is evidenced by the change in shape of the
spectrum at the highest energies. The fit to the spectrum requires that at
least one source be located relatively nearby at Mpc away from the
Milky Way. We discuss the origin of magnetic fields in the Local Supercluster
and the observable predictions of this model.Comment: 11 pages, 2 figures, submitted to PR
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