scholarly journals Observational Aspects of Galactic Magnetic Fields

1970 ◽  
Vol 39 ◽  
pp. 150-167 ◽  
Author(s):  
G. L. Verschuur
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Field Model ◽  
Continuum Emission ◽  
Radio Sources ◽  
Galactic Magnetic Fields ◽  
The Galaxy ◽  
Magnetic Field Model ◽  
Galactic Radio ◽  
Polarized Radiation

I will review the impressive advances in the observations of the galactic magnetic field made since the time of van de Hulst's review at the 1966 Noordwijk Symposium (van de Hulst, 1967). Most of these observations are so recent that the consequences have not yet been worked out very well and are in need of discussion. Luckily the emphasis in the present Symposium, unlike that in many others, is on discussion. For this reason I will not hesitate to include in my review provocative speculations. I will base my discussion on Mathewson's (1968) elegant magnetic field model, consisting of a local field in the form of a sheared helix, superimposed on a large scale longitudinal field. I will include the criticism of this model by Gardner et al. (1969b). Mathewson has succeeded in accounting for such data as the distribution of background polarized radiation from the Galaxy, the distribution of rotation measures of extra-galactic radio sources and even the spurs and ridges in galactic continuum emission. There are critics who inherently distrust models that account for too many things at one time, but I feel that we should try to account for as many things as possible with the least number of models. Mathewson has succeeded in uniting much data and I will only add a few pieces to his model.

scholarly journals F. Magnetic Fields, Pulsars, X-Ray And Gamma-Ray Emission

1985 ◽  
Vol 19 (1) ◽  
pp. 431-435
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Gamma Ray ◽  
Logarithmic Spiral ◽  
Radio Sources ◽  
Galactic Magnetic Field ◽  
Rotation Measure ◽  
The Galaxy ◽  
Magnetic Field Model ◽  
Characteristic Features

During the triennium under review many papers reported on studies of the structure of the galactic magnetic field. Andreasyan used rotation measures (RM) of large samples of extra-galactic radio sources and pulsars (29.156.001) or radio sources (32.156.002), and Inoue and Tabara (31.156.011) used in addition optical polarization of stars to investigate the direction of the large-scale regular magnetic field. Thomson and Nelson analyse the RMs of 459 extragalactic sources (32. 161.001) to determine the best fit parameters for a galactic magnetic-field model, and find agreement with their earlier work using pulsars (27.156.009). Similarly, Sofue and Fujimoto (33.155.011) show that the characteristic features of the RM distribution on the sky are well reproduced by a model in which the magnetic field is in a bisymmetric, two-armed logarithmic spiral configuration. Finally, Welter, Perry and Kronberg (37.159.096) present a statistical analysis of the (Galaxy-corrected) residual rotation measure (RRM) of 116 QSOs.

scholarly journals A bisymmetric spiral magnetic field in the Milky Way

1985 ◽  
Vol 106 ◽  
pp. 251-252
Author(s):  
Y. Sofue ◽  
M. Fujimoto
Keyword(s):  
Magnetic Field ◽  
Faraday Rotation ◽  
Large Scale ◽  
Milky Way ◽  
Radio Sources ◽  
Extragalactic Radio Sources ◽  
Large Scale Magnetic Field ◽  
Rotation Measure ◽  
The Galaxy ◽  
Field Lines

The distribution of Faraday rotation measure (RM) of extragalactic radio sources shows that a large-scale magnetic field in the Galaxy is oriented along the spiral arms. The field lines change direction from one arm to the next in the inter-arm region.

scholarly journals The effects of drift and winds on the propagation of Galactic cosmic rays

2021 ◽  
Author(s):  
A AL-Zetoun ◽  
A Achterberg
Keyword(s):  
Magnetic Field ◽  
Cosmic Rays ◽  
Field Model ◽  
Galactic Cosmic Rays ◽  
Galactic Magnetic Field ◽  
Galactic Wind ◽  
Wind Speeds ◽  
Field Diffusion ◽  
The Galaxy ◽  
Magnetic Field Model

Abstract We study the effects of drift motions and the advection by a Galactic wind on the propagation of cosmic rays in the Galaxy. We employ a simplified magnetic field model, based on (and similar to) the Jansson-Farrar model for the Galactic magnetic field. Diffusion is allowed to be anisotropic. The relevant equations are solved numerically, using a set of stochastic differential equations. Inclusion of drift and a Galactic wind significantly shortens the residence time of cosmic rays, even for moderate wind speeds.

scholarly journals A novel analytical model of the magnetic field configuration in the Galactic center

2020 ◽  
Vol 644 ◽  
pp. A71
Author(s):  
M. Guenduez ◽  
J. Becker Tjus ◽  
K. Ferrière ◽  
R.-J. Dettmar
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Field Model ◽  
Galactic Center ◽  
Cosmic Ray ◽  
Field Structure ◽  
Magnetic Field Structure ◽  
Center Region ◽  
Magnetic Field Model ◽  
The Magnetic Field

Context. Cosmic-ray propagation is strongly dependent on the large-scale configuration of the Galactic magnetic field. In particular, the Galactic center region provides highly interesting cosmic-ray data from gamma-ray maps and it is clear that a large fraction of the cosmic rays detected at Earth originate in this region of the Galaxy. Yet because of confusion from line-of-sight integration, the magnetic field structure in the Galactic center is not well known and no large-scale magnetic field model exists at present. Aims. In this paper, we develop a magnetic field model, derived from observational data on the diffuse gas, nonthermal radio filaments, and molecular clouds. Methods. We derive an analytical description of the magnetic field structure in the central molecular zone by combining observational data with the theoretical modeling of the basic properties of magnetic fields. Results. We provide a first description of the large-scale magnetic field in the Galactic center region. We present first test simulations of cosmic-ray propagation and the impact of the magnetic field structure on the cosmic-ray distribution in the three dimensions. Conclusions. Our magnetic field model is able to describe the main features of polarization maps; it is particularly important to note that they are significantly better than standard global Galactic magnetic field models. It can also be used to model cosmic-ray propagation in the Galactic center region more accurately.

scholarly journals A case study of the plasma in the magneto-sheath using the numerical magnetosheath-magnetosphere model and THEMIS measure-ments

2018 ◽  
Vol 145 ◽  
pp. 03004
Author(s):  
Polya Dobreva ◽  
Olga Nitcheva ◽  
Monio Kartalev
Keyword(s):  
Magnetic Field ◽  
Field Model ◽  
Specific Aspect ◽  
Plasma Parameters ◽  
Ion Density ◽  
Magnetic Field Model ◽  
Wind Spacecraft ◽  
The Mean ◽  
The Magnetic Field

This paper presents a case study of the plasma parameters in the magnetosheath, based on THEMIS measurements. As a theoretical tool we apply the self-consistent magnetosheath-magnetosphere model. A specific aspect of the model is that the positions of the bow shock and the magnetopause are self-consistently determined. In the magnetosheath the distribution of the velocity, density and temperature is calculated, based on the gas-dynamic theory. The magnetosphere module allows for the calculation of the magnetopause currents, confining the magnetic field into an arbitrary non-axisymmetric magnetopause. The variant of the Tsyganenko magnetic field model is applied as an internal magnetic field model. As solar wind monitor we use measurements from the WIND spacecraft. The results show that the model quite well reproduces the values of the ion density and velocity in the magnetosheath. The simlicity of the model allows calulations to be perforemed on a personal computer, which is one of the mean advantages of our model.

CO2 — A Champ Magnetic Field Model

2003 ◽  
pp. 220-225 ◽  
Author(s):  
Richard Holme ◽  
Nils Olsen ◽  
Martin Rother ◽  
Hermann Lühr
Keyword(s):  
Magnetic Field ◽  
Field Model ◽  
Magnetic Field Model

By Cam: A Multipole Magnetic Field Model

1995 ◽  
pp. 426-426 ◽  
Author(s):  
Paul A. Mason ◽  
G. Chanmugam ◽  
I. L. Andronov ◽  
S. V. Koleskinov ◽  
E. P. Pavlenko ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Field Model ◽  
Magnetic Field Model

scholarly journals Retrieving lithospheric magnetisation distribution from magnetic field models

2019 ◽  
Author(s):  
V Lesur ◽  
F Vervelidou
Keyword(s):  
Magnetic Field ◽  
Cost Function ◽  
Spherical Harmonic ◽  
Field Model ◽  
Harmonic Model ◽  
Whole Process ◽  
Magnetic Field Model ◽  
The Cost ◽  
Spherical Harmonic Model ◽  
The Magnetic Field

Summary We investigate to which extent the radially averaged magnetisation of the lithosphere can be recovered from the information content of a spherical harmonic model of the generated magnetic field when combined with few simple hypotheses. The results obtained show firstly that a hypothesis of magnetisation induced by a field of internal origin, even over a localised area, is not sufficient to recover uniquely the radially averaged magnetisation and, secondly, that this magnetisation can be recovered when a constant magnetisation direction is assumed. An algorithm to recover the magnetisation direction and distribution is then described and tested over a synthetic example. It requires to introduce a cost function that vanishes when estimated in a system of coordinates with its Z axis aligned with the magnetisation direction. Failing to find a vanishingly small value for the cost function is an indication that a constant magnetisation direction is not a valid hypothesis for the studied magnetic field model. The range of magnetisation directions that are compatible with the magnetic field model and a given noise level, can also be estimated. The whole process is illustrated by analysing a local, isolated maximum of the Martian magnetic field.

scholarly journals Velocity-Magnetic Field Correlation of Pulsars

1996 ◽  
Vol 160 ◽  
pp. 49-50
Author(s):  
Naoki Itoh ◽  
Takemi Kotouda
Keyword(s):  
Magnetic Field ◽  
Constant Magnetic Field ◽  
Field Model ◽  
Transverse Velocity ◽  
Distribution Model ◽  
Recent Measurement ◽  
Apparent Correlation ◽  
Magnetic Field Model ◽  
Field Correlation ◽  
The Magnetic Field

Monte Carlo simulations of the evolution of pulsars are carried out in order to compare with the recent measurement of the pulsar transverse velocity by Lyne & Lorimer (1994). The new electron density distribution model of Taylor & Cordes (1993) is adopted in the simulation. Accurate pulsar orbits in the Galactic gravitational field are calculated. It is found that the constant magnetic field model of pulsars can account for the new measurement of the pulsar transverse velocity and the apparent correlation between the strength of the magnetic field and the transverse velocity of the pulsars. The present finding confirms the validity of the constant magnetic field model of pulsars and consolidates the idea that the apparent correlation between the strength of the magnetic field and the transverse velocity of the pulsars is caused by observational selection effects.

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