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What can be learned about competing acceleration models from multiwavelength observations?
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Nicole Vilmer Submitted: 2002-07-19 07:45
We review the available evidence from various wavelength ranges, alone and in combination, bearing on solar particle acceleration. Radio, X-ray and gamma-ray observations yield direct information on solar ion and electron acceleration at the Sun. We describe the main spectral features in the
X/gamma domain, outline the means by which they yield information on accelerated particles, and summarise results obtained using them on numbers and energies of flare fast ions and electrons. Relative numbers and energy content
of electrons and ions may vary from flare to flare, and in the course of a single event. In general, both electronic and ionic species appear to embody significant fractions of the total flare energy and either can be dominant,
although there is great uncertainty over accelerated particle minimum energies.Rapid fluctuations in X/gamma-rays point to a fragmented accelerator, acting
on timescales of 100 ms or less, even after particle transport effects have been considered. Millimeter wave observations also reveal spatial fragmentation. Together
with distributions of overall event size, such fragmentation suggests a scale-invariant energy release process, such as would occur in a state of Self-Organised Criticality. There is good evidence from X/gamma and cm/mm observations for hardening of the electron distribution towards the MeV energy range. Intercomparisons of X/gamma rays and cm/mm wave observations emphasise the importance of MeV energy range electrons in the latter. 'Electron-rich' events, characterised by a hard electron population extending to relativistic energies, may occur during individual flares. Existing instrumental capabilities mean that the absence of gamma-ray lines does not rule out significant,
simultaneous ion acceleration. Radio observations indicate these spectral changes are associated with changes in spatial structure. Spatially resolved radio observations
indicate that primary particle acceleration takes place moderately high in the corona (107 to 108 m), and have recently been made to yield information
on accelerated electron pitch angle distribution. Throughout, we emphasise questions on which the unprecedented capabilities of the RHESSI mission will shed
new light.
Authors: Nicole Vilmer and Alexander L. MacKinnon
Projects:
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Publication Status: to be published in Lecture Notes in Physics
Last Modified: 2002-07-19 07:45
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