Theory of gyroresonance and free-free emissions from non-maxwellian quasi-steady-state electron distributions

Gregory Fleishman, Alexey A. Kuznetsov

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19 Scopus citations


Currently there is a concern about the ability of the classical thermal (Maxwellian) distribution to describe quasi-steady-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 τ for kappa-distribution, but decreases with τ for n-distribution. This property has a remarkable consequence allowing a straightforward observational test: the GR radio emission from the non-Maxwellian 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.

Original languageEnglish (US)
Article number77
JournalAstrophysical Journal
Issue number2
StatePublished - Feb 1 2014

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Sun: corona
  • Sun: magnetic fields
  • Sun: radio radiation


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