Title: Identification of multiple hard X-ray sources in solar flares: A Bayesian analysis of the February 20 2002 event,
Abstract: The hard X-ray emission in a solar flare is typically characterized by a
number of discrete sources, each with its own spectral, temporal, and spatial
variability. Establishing the relationship amongst these sources is critical to
determine the role of each in the energy release and transport processes that
occur within the flare. In this paper we present a novel method to identify and
characterize each source of hard X-ray emission. The method permits a
quantitative determination of the most likely number of subsources present, and
of the relative probabilities that the hard X-ray emission in a given subregion
of the flare is represented by a complicated multiple source structure or by a
simpler single source. We apply the method to a well-studied flare on
2002~February~20 in order to assess competing claims as to the number of
chromospheric footpoint sources present, and hence to the complexity of the
underlying magnetic geometry/toplogy. Contrary to previous claims of the need
for multiple sources to account for the chromospheric hard X-ray emission at
different locations and times, we find that a simple
two-footpoint-plus-coronal-source model is the most probable explanation for
the data. We also find that one of the footpoint sources moves quite rapidly
throughout the event, a factor that presumably complicated previous analyses.
The inferred velocity of the footpoint corresponds to a very high induced
electric field, compatible with those in thin reconnecting current sheets.