THEORY OF GYRORESONANCE AND FREE-FREE EMISSIONS FROM NON-MAXWELLIAN QUASI-STEADY-STATE ELECTRON DISTRIBUTIONS

Currently there is a concern about the ability of the classical thermal (Maxwellian) distribution to describe quasisteady-state plasma in the solar atmosphere, including active regions. In particular, other distributions have been proposed to better fit observations, for example, kappa- and n-distri...

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Bibliographic Details
Published in:The Astrophysical journal 2014-02, Vol.781 (2), p.1-16
Main Authors: Fleishman, Gregory D, Kuznetsov, Alexey A
Format: Article
Language:English
Subjects:
ABSORPTION
ASTROPHYSICS
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
BRIGHTNESS
Brightness temperature
COMPARATIVE EVALUATIONS
DISTRIBUTION
ELECTRONS
EMISSION
Emission analysis
EMISSIVITY
MAGNETIC FIELDS
Mathematical analysis
PLASMA
POLARIZATION
Radio emission
Remote sensing
SOLAR ATMOSPHERE
STEADY-STATE CONDITIONS
SUN
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Summary:Currently there is a concern about the ability of the classical thermal (Maxwellian) distribution to describe quasisteady-state plasma in the solar atmosphere, including active regions. In particular, other distributions have been proposed to better fit observations, for example, kappa- and n-distributions. If present, these distributions will generate radio emissions with different observable properties compared with the classical gyroresonance (GR) or free-free emission, which implies a way of remotely detecting these non-Maxwellian distributions in the radio observations. Here we present analytically derived GR and free-free emissivities and absorption coefficients for the kappa- and n-distributions, and discuss their properties, which are in fact remarkably different from each other and from the classical Maxwellian plasma. In particular, the radio brightness temperature from a gyrolayer increases with the optical depth [tau] for kappa-distribution, but decreases with [tau] for n-distribution. This property has a remarkable consequence allowing a straightforward observational test: the GR radio emission from the nonMaxwellian distributions is supposed to be noticeably polarized even in the optically thick case, where the emission would have strictly zero polarization in the case of Maxwellian plasma. This offers a way of remote probing the plasma distribution in astrophysical sources, including solar active regions as a vivid example.
ISSN:0004-637X
1538-4357
DOI:10.1088/0004-637X/781/2/77