Charge state distributions of iron in gradual solar energetic particle events

The energy and charge spectra of Fe ions accelerated in gradual events are calculated numerically. Our results are compared with the available observations. Stripping of Fe ions by thermal electrons and protons during ion acceleration in the solar corona results in the dependence of mean charge barq_Feon energy. We consider the influence of varying plasma parameters (temperature T, number density N, and spectral index of turbulence S) on the charge distribution of iron. Our calculations indicate T10⁶ K and N(0.5–1)×10¹⁰ cm^–3at the accelerating site, provided the characteristic acceleration time is about 1 s. The calculated charge spectra for S>2 and S<2 turn out to be different, but some theoretical and experimental uncertainties do not yet allow this parameter to be extracted from observational data. The theoretically obtained charge distributions of Fe could be important in the light of ACE spacecraft data which are currently available for analysis.