1,651 research outputs found
An Equilibrium State for the Interstellar Gas and Magnetic Field
Equilibrium state for interstellar gas and magnetic fiel
Unstable magnetosonic waves in a relativistic plasma
Linearized equations for unstable waves in relativistic plasm
On the transport of charged particles in turbulent fields: comparison of an exact solution with the quasilinear approximation
The problem of charged-particle transport in a magnetic field which is solely a function of time is solved. The solution is obtained exactly, to all orders in the field, in the limit of large wavelengths normal to the magnetic field. It is shown that the usual quasilinear, Fokker-Planck approximation is equal to the exact solution in the limit of times large compared with the correlation time of the fluctuating field. This is just the regime where the approximation has been used in the past, and this special case thus gives some support to the standard approximation techniques
Why do leaky-box models work so fine?
By introducing the concept of the age distribution of cosmic rays it is possible to decouple spatial from momentum transport, and simple leaky-box type equations result. The influence of spatial inhomogeneities, geometries, and source distributions enters the spatially homogeneous, infinite (i.e., leaky box) problem through appropriate mean lifetimes. A precise prescription of how to obtain these mean lifetimes, i.c., for comparison with data measured in the vicinity of the solar system they have to be calculated from the age distribution at the spatial position of the observer
Evidence for a dynamical halo around the edge-on galaxy NGC 4631
Radio continuum observations at five frequencies between 327 MHz and 10.7 GHz of the edge on galaxy NGC 4631 confirm the prediction concerning the frequency dependence of the halo extent and the spatial variations of the radio spectral indices in the dynamical halo model made by Lerche and Schlickeiser. The measurements are presented, and a detailed comparison with theoretical predictions is made
Explanation of the secondary to primary ratio within the continuous Fermi accelerator model
The secondary to primary ratio in galactic cosmic radiation at relativistic momenta is calculated in a model, where the primaries are continuously accelerated from the thermal galactic background medium by 1st and 2nd order Fermi acceleration. It is shown that the measured decrease with momentum does not exclude that cosmic rays are accelerated in the interstellar medium as a whole. Once a momentum dependence of the mean lifetime and the different spatial source distributions are adequately taken into account, the measured decreasing ratio can be explained
Influence of the source distribution on the age distribution of galactic cosmic rays
The age distribution of galactic cosmic rays in the diffusion approximation is calculated. The influence of the scale height of the spatial source distribution on the mean age of particles arriving at the solar system is discussed. The broader the source distribution with respect to the galactic plane, the longer the mean age. This result provides a natural explanation for the shorter mean age of secondary cosmic rays compared to primary cosmic rays necessary for the understanding of the observed secondary/primary ratio
An Initial Value Problem for Oscillations of the Interstellar Gas
Initial value problem for oscillations in interstellar ga
Modification of cosmic-ray energy spectra by stochastic acceleration
Context: Typical space plasmas contain spatially and temporally variable
turbulent electromagnetic fields. Understanding the transport of energetic
particles and the acceleration mechanisms for charged particles is an important
goal of today's astroparticle physics. Aims: To understand the acceleration
mechanisms at the particle source, subsequent effects have to be known.
Therefore, the modification of a particle energy distribution, due to
stochastic acceleration, needs to be investigated. Methods: The diffusion in
momentum space was investigated by using both a Monte-Carlo simulation code and
by analytically solving the momentum-diffusion equation. For simplicity, the
turbulence was assumed to consist of one-dimensional Alfven waves. Results:
Using both methods, it is shown that, on average, all particles with velocities
comparable to the Alfven speeds are accelerated. This influences the energy
distribution by significantly increasing the energy spectral index.
Conclusions: Because of electromagnetic turbulence, a particle energy spectrum
measured at Earth can drastically deviate from its initial spectrum. However,
for particles with velocities significantly above the Alfven speed, the effect
becomes negligible.Comment: 10 pages, 6 figures, accepted for publication in Astronomy &
Astrophysic
Radio Cerenkov radiation from a primary cosmic ray
Radiation field of primary cosmic ray moving in straight line motion in earth atmospher
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