Iron Charge State Distributions for Four Large SEP Events in the Energy Range 0.23 0.23-0.33 MeV/nuc: Implications for Source Populations

摘要

Charge state measurements of solar energetic particles (SEP) provide diagnostic information about the source pop populations and acceleration mechanisms and their locations in SEP events. The SEPICA instrument on lations board the ACE spacecraft can directly measure the ionic charge state for SEP iron ions with energies below 0.6 MeV/nuc. The direct measurement technique yields not only the mean charge of iron ions for an event, but the charge state di dis- stribution as well. tribution We determined event event-averaged iron charge state distributions in the energy range 0.23 to 0.33 MeV/nuc for several large (gradual) SEP events. We find a large variability of iron charge distributions, ranging from distributions compatible with a coronal so source at ~1MK to distributions with a pronounced tail at high charge urce states, suggesting the presence of multiple sources or additional effects, such as stripping in the low corona. We pr present some typical examples and discuss the implications for propagat sent propagation and acceleration effects.