Observations of heavy ion charge spectra in CME driven gradual solar energetic particle events

Abstract

Recent measurements by SAMPEX and SEPICA/ACE have delivered evidence that a class of gradual Coronal Mass Ejection (CME) related solar energetic particle events (SEP) exists, characterised by energy dependent charge distributions. We investigate this aspect of the energization and charging phenomena in CME driven particle events by analysis of data from two instruments: SEPICA/ACE and STOF/SOHO. Combined they cover the energy range from ∼ 0.02 to 0.60 MeV/amu for O and Fe. The investigation of newly available events and the extension of the energy range to lower values by STOF data seems to confirm that the energy dependence of charge states may be of more general nature than hitherto assumed. Now we can extend the observed energy range to enable future comparisons with values typical for the solar wind. A more thorough comparison between experiment and models on particle acceleration in gradual CME events becomes possible and will contribute to the correct interpretation of the formation of the observed charge spectra. Longstanding questions concerning the seed populations, acceleration sites, stripping mechanisms in these events can be re-examined.