Interpretation of magnetic-energy density with the Amperian model

1974 ◽  
Vol 29 (1) ◽  
pp. 14-18
Author(s):  
E. Engels ◽  
H. Pauwels
Keyword(s):  
Energy Density ◽  
Magnetic Energy ◽  
Magnetic Energy Density

scholarly journals Can the Local Bubble explain the radio background?

2021 ◽  
Vol 502 (2) ◽  
pp. 2807-2814
Author(s):  
Martin G H Krause ◽  
Martin J Hardcastle
Keyword(s):  
Magnetic Field ◽  
Energy Density ◽  
Radio Emission ◽  
Magnetic Energy ◽  
Cosmic Ray ◽  
Observational Constraints ◽  
Local Bubble ◽  
Magnetic Energy Density ◽  
Magnetic Field Model ◽  
Radio Background

ABSTRACT The ARCADE 2 balloon bolometer along with a number of other instruments have detected what appears to be a radio synchrotron background at frequencies below about 3 GHz. Neither extragalactic radio sources nor diffuse Galactic emission can currently account for this finding. We use the locally measured cosmic ray electron population, demodulated for effects of the Solar wind, and other observational constraints combined with a turbulent magnetic field model to predict the radio synchrotron emission for the Local Bubble. We find that the spectral index of the modelled radio emission is roughly consistent with the radio background. Our model can approximately reproduce the observed antenna temperatures for a mean magnetic field strength B between 3 and 5 nT. We argue that this would not violate observational constraints from pulsar measurements. However, the curvature in the predicted spectrum would mean that other, so far unknown sources would have to contribute below 100 MHz. Also, the magnetic energy density would then dominate over thermal and cosmic ray electron energy density, likely causing an inverse magnetic cascade with large variations of the radio emission in different sky directions as well as high polarization. We argue that this disagrees with several observations and thus that the magnetic field is probably much lower, quite possibly limited by equipartition with the energy density in relativistic or thermal particles (B = 0.2−0.6 nT). In the latter case, we predict a contribution of the Local Bubble to the unexplained radio background at most at the per cent level.

scholarly journals Absorption of Curvature Radiation

1979 ◽  
Vol 32 (2) ◽  
pp. 49 ◽  
Author(s):  
VV Zheleznyakov ◽  
VE Shaposhnikov
Keyword(s):  
Magnetic Field ◽  
Energy Density ◽  
Optical Depth ◽  
Magnetic Energy ◽  
Particle Energy ◽  
Relativistic Electrons ◽  
Magnetic Energy Density ◽  
Curvature Radiation ◽  
Maser Effect ◽  
Field Lines

The reabsorption of curvature radiation, i.e. radiation from relativistic electrons moving along curved magnetic field lines, is discussed. The optical depth for the ray path is calculated by use of the Einstein coefficients. It is shown that the optical depth becomes negative (maser effect) if transitions between Landau levels are absent. However, maser action is ineffective if the energy density of the relativistic particles is less than that of the magnetic field. For pulsar radio emission the magnetic energy density is assumed to exceed the particle energy density, so the observed emission cannot be coherent curvature radiation.

Possibility of an inverse cascade of magnetic helicity in magnetohydrodynamic turbulence

1975 ◽  
Vol 68 (4) ◽  
pp. 769-778 ◽  
Author(s):  
U. Frisch ◽  
A. Pouquet ◽  
J. LÉOrat ◽  
A. Mazure
Keyword(s):  
Energy Density ◽  
Large Scale ◽  
Magnetic Energy ◽  
Three Dimensional ◽  
Magnetic Helicity ◽  
Kinetic Energy Density ◽  
Magnetohydrodynamic Turbulence ◽  
Magnetic Energy Density ◽  
Upper Limit ◽  
Cross Correlations

Some of the consequences of the conservation of magnetic helicity$\int \rm{a.b}\it{d}^{\rm{3}}\rm{r\qquad (a\; =\; vector\; potential\; of\; magnetic\; field\; b)}$for incompressible three-dimensional turbulent MHD flows are investigated. Absolute equilibrium spectra for inviscid infinitely conducting flows truncated at lower and upper wavenumberskminandkmaxare obtained. When the total magnetic helicity approaches an upper limit given by the total energy (kinetic plus magnetic) divided bykmin, the spectra of magnetic energy and helicity are strongly peaked nearkmin; in addition, when the cross-correlations between the velocity and magnetic fields are small, the magnetic energy density nearkmingreatly exceeds the kinetic energy density. Several arguments are presented in favour of the existence of inverse cascades of magnetic helicity towards small wavenumbers leading to the generation of large-scale magnetic energy.

scholarly journals Radio-Source Spectra and their Time Variations

1968 ◽  
Vol 1 ◽  
pp. 371-372
Author(s):  
K.I. Kellermann ◽  
I.I.K. Pauliny-Toth
Keyword(s):  
Energy Density ◽  
Flux Density ◽  
Magnetic Energy ◽  
Relativistic Electrons ◽  
Low Frequencies ◽  
High Frequencies ◽  
Magnetic Energy Density ◽  
Straight Line ◽  
Time Variations ◽  
Compact Sources

During the past few years there has been a large increase in the available data on the spectra of radio sources, particularly at short wavelengths, where a number of sources have shown unexpectedly large time variations, with time-scales of 1 year or less.The simple power-law spectrum, which is a straight line on a log-log plot of flux density against frequency, is shown by about 30% of sources. Most sources have a spectrum with negative curvature, which steepens at high frequencies. Many have a sharp cut-off, which is almost certainly due to synchrotron self-absorption, at low frequencies. In several of these sources, such as 3C 48, 3C 147 and 3C 295, the spectrum begins to flatten at a considerably higher frequency than the cut-off frequency. This flattening is too sharp to be caused by a change in the energy distribution of the electrons and is probably due to parts of the source becoming optically thick at higher frequencies. Some sources have components which are optically thick even at centimetre wavelengths. These must have angular sizes of 10−3″ or less. The energy density in relativistic electrons in these compact sources is much larger than the magnetic-energy density, so that the source cannot be stable and variations in the flux density are to be expected.

scholarly journals Relativistic Modifications in Galactic Rotation Curves under a Toroidal Galactic Field

2021 ◽  
Author(s):  
Babur M. Mirza
Keyword(s):  
Energy Density ◽  
Galactic Center ◽  
Magnetic Energy ◽  
Rotational Velocity ◽  
Galactic Rotation ◽  
Axially Symmetric ◽  
Rotation Curves ◽  
Observable Universe ◽  
Magnetic Energy Density ◽  
Dynamics Of Galaxies

Abstract Rotational dynamics of galaxies exhibits an increase beyond the Keplerian velocity which corresponds to a missing mass up to six times the dynamic mass in the observable universe. In this paper we show that the observed increase in galactic rotation velocities is a general relativistic effect resulting from the combined effect of toroidal magnetic energy density in galaxies and spacetime dragging due to the rotating compact mass in galactic center. The effect of magnetic energy density on spacetime vorticity is derived from Maxwell equations in axially symmetric spacetime where the dragging effects are shown to extend farther in the galactic disc via the toroidal field, modifying the rotational speed of the galactic matter. This is shown to lead to the diverse rotation curves of spiral galaxies, along with the Tully-Fisher relation for total galactic mass and maximum rotational velocity.

scholarly journals Tailward Propagation of Magnetic Energy Density Variations With Respect to Substorm Onset Times

2018 ◽  
Vol 123 (6) ◽  
pp. 4741-4754 ◽  
Author(s):  
John C. Coxon ◽  
Mervyn P. Freeman ◽  
Caitriona M. Jackman ◽  
Colin Forsyth ◽  
I. Jonathan Rae ◽  
...  
Keyword(s):  
Energy Density ◽  
Magnetic Energy ◽  
Substorm Onset ◽  
Magnetic Energy Density

Note on the magnetic energy density

1982 ◽  
Vol 50 (8) ◽  
pp. 758-759 ◽  
Author(s):  
N. Gauthier ◽  
H. D. Wiederick
Keyword(s):  
Energy Density ◽  
Magnetic Energy ◽  
Magnetic Energy Density

Nonlinear waves and shocks in relativistic two-fluid hydrodynamics

2012 ◽  
Vol 78 (3) ◽  
pp. 295-302 ◽  
Author(s):  
L. HAIM ◽  
M. GEDALIN ◽  
A. SPITKOVSKY ◽  
V. KRASNOSELSKIKH ◽  
M. BALIKHIN
Keyword(s):  
Energy Density ◽  
Shock Front ◽  
Magnetic Energy ◽  
Ambient Medium ◽  
Nonlinear Effects ◽  
Magnetic Energy Density ◽  
Fluid Analysis ◽  
Relativistic Shocks ◽  
Wide Range ◽  
Two Fluid

AbstractRelativistic shocks are present in a number of objects where violent processes are accompanied by relativistic outflows of plasma. The magnetization parameter σ = B2/4πnmc2 of the ambient medium varies in wide range. Shocks with low σ are expected to substantially enhance the magnetic fields in the shock front. In non-relativistic shocks the magnetic compression is limited by nonlinear effects related to the deceleration of flow. Two-fluid analysis of perpendicular relativistic shocks shows that the nonlinearities are suppressed for σ≪1 and the magnetic field reaches nearly equipartition values when the magnetic energy density is of the order of the ion energy density, Beq2 ~ 4πnmic2γ. A large cross-shock potential eφ/mic2γ0 ~ B2/Beq2 develops across the electron–ion shock front. This potential is responsible for electron energization.

scholarly journals The Origin of Interplanetary Sectors

1980 ◽  
Vol 91 ◽  
pp. 67-72
Author(s):  
Kenneth H. Schatten
Keyword(s):  
Magnetic Field ◽  
Energy Density ◽  
Magnetic Energy ◽  
Coronal Magnetic Field ◽  
Restrictive Assumption ◽  
Plasma Energy ◽  
Magnetic Energy Density ◽  
Physical Phenomena ◽  
The Magnetic Field ◽  
Shed Light

The coronal magnetic models of Altschuler and Newkirk (1969), Schatten, Wilcox and Ness (1969), and Schatten (1971) that allowed calculations of the coronal magnetic field from the observed photospheric magnetic field shed light on the origin of sectors. Figure 1 from Schatten's (1971) “Current Sheet Model” is a schematic representation of these similar models. There are three distinct regions in these models where different physical phenomena occur. The photosphere, where the magnetic fields are governed by the detailed motions and currents in the plasma is considered a boundary condition for the model. Above the photosphere, the plasma density diminishes very rapidly with only moderate decreases in the magnetic energy density. This results in the middle region where the magnetic energy density is greater than plasma energy density and hence controls the configuration. One may then utilize the force-free condition, j × B = 0, and in fact make the more restrictive assumption that this region is current free. The magnetic field in this region can be derived from a solution to the Laplace equation.

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