The Role of Inverse Compton Scattering in Solar Coronal Hard X-ray and γ-ray Sources
Abstract
We consider the role of inverse Compton scattering (ICS) as a means of producing coronal hard X-ray (HXR) and continuum γ-ray sources during solar flares. Coronal HXR and continuum γ-ray emission observed during solar flares has been interpreted in terms of thin-target bremsstrahlung emission. In one case, this interpretation leads to the conclusion that the number of energetic electrons required to account for the coronal HXR source must be large, implying that essentially all electrons in the source must be accelerated to energies ≥ 16 keV. In other cases, the spectral index of the photon spectrum of γ-ray sources approaches the theoretical limit for bremsstrahlung emission (α ~ 1.5 - 2). Here we investigate ICS in both the fully relativistic and mildly relativistic regimes as an alternative to non-thermal bremsstrahlung. It is known that relativistic electrons are produced during powerful flares; these are capable of up-scattering soft photospheric photons to HXR energies. Previously overlooked is the fact that mildly relativistic electrons, generally produced in much greater numbers in flares of all sizes, can up-scatter EUV/SXR photons to HXR energies. We also explore ICS on anisotropic electron distributions and show that the resulting emission can be significantly enhanced over the case of scattering on an isotropic electron distribution. We apply our results to a selection of coronal HXR and γ-ray events and find that in some cases the ICS mechanism is a viable alternative to non-thermal bremsstrahlung emission, particularly if the energetic population of electrons responsible for the emission is anisotropic.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFMSH44A..05C
- Keywords:
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- 7514 SOLAR PHYSICS;
- ASTROPHYSICS;
- AND ASTRONOMY / Energetic particles;
- 7519 SOLAR PHYSICS;
- ASTROPHYSICS;
- AND ASTRONOMY / Flares;
- 7554 SOLAR PHYSICS;
- ASTROPHYSICS;
- AND ASTRONOMY / X-rays;
- gamma rays;
- and neutrinos;
- 7847 SPACE PLASMA PHYSICS / Radiation processes