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Coronal sources of solar energetic particle events
The present picture of acceleration processes leading to solar energetic
particle (SEP) events distinguishes two sources in the solar corona: flares
are considered as generators of SEP events that are detected when the satellite
is well connected with the site of the H alpha signature, and large scale
shocks driven by fast coronal mass ejections (CMEs) are believed to accelerate
particles over a large range of heliocentric angles out of the coronal
plasma, leading to the largest and longest lasting SEP events. While such
a neat separation of accelerators is able to account for observed properties
such as the appparently bimodal distribution of ionization states (especially
Fe) and of abundance peculiarities at energies up to a few MeV per nucleon,
it also involves unproven assumptions: - that a single accelerator acts
at all energies, from suprathermal to relativistic, - that
flare-related acceleration operates only in a small volume and during
negligibly short duration with respect to the SEP event.
The present contribution attempts to review observational constraints
by comparing the time history of coronal particle acceleration with that
of protons and electrons detected between 0.3 and 1 AU. It is pointed out
that during the combined occurrence of CMEs and flares electrons may be
accelerated at, or transported to widely separated sites behind the CME,
and that there is some evidence on the co-evolution of these electron signatures
and energetic electrons and protons (>> 1 MeV/nucleon) detected in interplanetary
space. This suggests that a more complex scenario of coronal particle acceleration
may be required to understand SEP events than the distinction of flare
accelerated and shock accelerated particle populations.
Above is background material for archival reference only.