The nonMaxwellian continuum in the Xray, UV, and radio range
Abstract
Aims: We investigate the Xray, UV, and also the radio continuum arising from plasmas with a nonMaxwellian distribution of electron energies. The two investigated types of distributions are the κ and ndistributions.
Methods: We derived analytical expressions for the nonMaxwellian bremsstrahlung and freebound continuum spectra. The spectra were calculated using available crosssections. Then we compared the bremsstrahlung spectra arising from the different bremsstrahlung crosssections that are routinely used in solar physics.
Results: The behavior of the bremsstrahlung spectra for the nonMaxwellian distributions is highly dependent on the assumed type of the distribution. At flare temperatures and hard Xray energies, the bremsstrahlung is greatly increased for κdistributions and exhibits a strong highenergy tail. With decreasing κ, the maximum of the bremsstrahlung spectrum decreases and moves to higher wavelengths. In contrast, the maximum of the spectra for ndistributions increases with increasing n, and the spectrum then falls off very steeply with decreasing wavelength. In the millimeter radio range, the nonMaxwellian bremsstrahlung spectra are almost parallel to the thermal bremsstrahlung. Therefore, the nonMaxwellian distributions cannot be detected by offlimb observations made by the ALMA instrument. The freebound continua are also highly dependent on the assumed type of the distribution. For ndistributions, the ionization edges disappear and a smooth continuum spectrum is formed for n ≧ 5. Opposite behavior occurs for κdistributions where the ionization edges are in general significantly enhanced, with details depending on κ and T through the ionization equilibrium. We investigated how the nonMaxwellian κdistributions can be determined from the observations of the continuum and conclude that one can sample the lowenergy part of the distribution from the continuum.
Appendix A is available in electronic form at http://www.aanda.org
 Publication:

Astronomy and Astrophysics
 Pub Date:
 March 2012
 DOI:
 10.1051/00046361/201118345
 Bibcode:
 2012A&A...539A.107D
 Keywords:

 Sun: Xrays;
 gamma rays;
 Sun: radio radiation;
 radiation mechanisms: nonthermal;
 atomic processes