On the physical meaning of n-distributions in solar flares
1 Astronomical Institute of the Academy of Sciences of the Czech Republic, 25165 Ondřejov, Czech Republic
2 Dept. of Astronomy, Physics of the Earth and Meteorology, Faculty of Mathematics, Physics and Informatics, Comenius University, 84248 Bratislava, Slovak Republic
Received: 9 August 2011
Accepted: 28 October 2011
Aims. We investigate the physical meaning of the n-distributions detected in solar flares.
Methods. We consider a Maxwellian velocity distribution with a velocity drift. This distribution is analytically integrated to obtain the energy distribution, and its stability is investigated numerically using a fully electromagnetic particle-in-cell code.
Results. It is shown that the derived moving Maxwellian energy distribution is very similar to the n-distribution, especially in their high-energy parts. Both these distributions are mutually fitted and a relation between their parameters found. Contrary to the n-distribution, the moving Maxwellian distribution has a simple physical meaning, e.g., the electron component of the return current in the beam-plasma system. However, for high drift velocities of such a component, the moving Maxwellian distribution is unstable. Therefore to keep the form of this distribution similar to the n-distribution, some stabilization processes are necessary. If so, then the high intensities of the Si xiid 5.56 Å and 5.82 Å satellite lines and their evolution in solar flares can be explained by moving Maxwellian distributions instead of the n-distributions. Thus, our previous results connected with the n-distributions can be understood in a new, physically profound way.
Key words: Sun: flares / Sun: X-rays, gamma rays
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