Journal
ASTRONOMY & ASTROPHYSICS
Volume 529, Issue -, Pages -Publisher
EDP SCIENCES S A
DOI: 10.1051/0004-6361/201016329
Keywords
atomic processes; radiation mechanisms: non-thermal; Sun: corona; Sun: X-rays, gamma rays; instabilities
Categories
Funding
- Scientific Grant Agency, VEGA, Slovakia [1/0240/11]
- Grant Agency of the Academy of Sciences of the Czech Republic [IAA300030701]
- Grant Agency of the Czech Republic [205/09/1705, 205/09/1469]
- Comenius University [UK/398/2009, UK/237/2010]
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Context. The radiative-loss function is an important ingredient in the physics of the solar corona, transition region, and flares. Aims. We investigate the radiative losses due to the bound-bound transitions and bremsstrahlung for nonthermal kappa- and n-distributions. Methods. The bound-bound radiative losses are computed by integrating synthetic spectra. An analytical expression is derived for nonthermal bremsstrahlung. The bremsstrahlung is computed numerically using accurate values of the free-free Gaunt factor. Results. We find that the changes in radiative-loss functions due to nonthermal distributions are several times greater than the errors due to the missing contribution of the free-bound continuum or errors in atomic data. For kappa-distributions, the radiative-loss functions are in general weaker than for Maxwellian distribution, with a few exceptions caused by the behavior of Fe. The peaks of the radiative-loss functions are in general flatter. The situation is opposite for n-distributions, for which the radiative-loss functions have higher and narrower peaks. Local minima and maxima of the radiative-loss functions may also be shifted. The contribution from bremsstrahlung only changes by a few percent except in the extreme nonthermal case of kappa=2. Stability analysis reveals that the X-ray loops are stable against the radiatively-driven thermal instability.
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