Solar Physics Division Meeting 2000, June 19-22
Session 2. Corona, Solar Wind, Flares, CMEs, Solar-stellar, Instrumentation, Other
Display, Chair: J. Krall, Monday-Thursday, June 19, 2000, 8:00am-6:00pm, Forum Ballroom

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[2.45] Evolution and Statistics of the Loop-top hard X-ray emission

T. Q. Donaghy, V. Petrosian (Stanford University), J. McTiernan (Univ. of California, Space Sciences Lab)

The discovery of hard X-ray sources located at or above the top of a flaring loop, by the Yohkoh satellite was a great leap forward in understanding the mechanisms driving solar flares. For the first time we have been able to probe the complex flare structure and can begin to decipher the acceleration process. The HESSI satellite, with its superior angular, temporal and spectral resolution should extend our knowledge even further. Recently we (Petrosian & Donaghy, ApJ, 1999) have demonstrated the importance of these observations in constraining the acceleration parameters. Investigation of the temporal evolution of these features can provide further understanding of the underlying questions about particle acceleration and transportation.

Masuda (1994) performed the first analysis of such questions in presenting spatial analyses of ten limb flares seen by Yohkoh and temporal analyses for two of the ten. However, there are several questions which require further study, specifically with flares involving multiple impulsive peaks and/or multiple sources. For example, do loop-top sources systematically appear during certain epochs of the impulsive phase of the flare? What is the relationship between different peaks in multiple peak-events? Why do some flares show no loop-top source at all? How are multiple foot-point sources incorporated into an acceleration + precipitation model? Does the data available support the current acceleration + precipitation models? What selection and bias effects are at work? In seeking to answer these questions we present 8 new events that conform to Masuda's selection criteria, as well as three others that are marginal, but interesting. These results will be presented.

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