Scattered Light: Inverse Compton Scattering and Coronal Hard X-ray Sources

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Nugget
Number:	157
1st Author:	B. Chen
2nd Author:	T. S. Bastian
Published:	17 July 2011
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Introduction

Hard X-ray (HXR) emission from solar flares typically comes from the lowest parts of the solar atmosphere (see earlier Nuggets such as this one). Truly coronal HXR emission has also been (rarely) observed since the early 1970s, but there has been renewed interest in these sources with the availability of HXR imaging and spectroscopy via Yohkoh/HXT and now of course RHESSI. In most cases, these coronal HXR sources can be explained by non-thermal bremsstrahlung emission. However, there are some cases where the source parameters required by the bremsstrahlung model can be extreme. For example, in a recently reported case [1] the interpretation of the coronal HXR source in terms of simple bremsstrahlung emission implies that all of the electrons in the source must have been accelerated to energies >16 keV. In other cases the spectral index of the HXR spectrum of the continuum γ-ray sources approaches its theoretical limit, an unexpected property that would be hard to explain. Motivated by these cases, we have explored the viability of inverse Compton scattering (ICS) as an alternative mechanism to non-thermal bremsstrahlung (see an earlier Nugget for more explanation).

References

[1] Measurements of the Coronal Acceleration Region of a Solar Flare