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Gamma-Ray Observations of Solar Flares with RHESSI Imaging Spectroscopy and the GRIPS instrument

  • Author(s): Duncan, Nicole
  • Advisor(s): Boggs, Steven
  • et al.

Solar flares can release ~1e33 ergs of power, accelerate particles to relativistic speeds, heat plasma to ~15 million K and catastrophically reorganize 1e5 km long field structures in 100s - 1000s of seconds. Magnetic reconnection of large-scale field structures in the corona are thought to power flares, but the precise mechanisms that convert the stored magnetic energy into particle kinetic energy are poorly understood.

Flare spectra in the 20 keV - 10 MeV energy range are rich with information that provide a window into the underlying physics of flare particle acceleration. This hard X-ray (HXR)/gamma-ray emission can be used to understand electron and ion dynamics, particle abundances and the ambient plasma conditions in solar flares. Enhanced imaging, spectroscopy and polarimetry of flare emissions in this energy range are needed to address the current era of particle acceleration and transport questions, including: What causes the spatial separation between HXR emission generated by relativistic electrons and the gamma-ray line emission from energetic ions? How anisotropic are the relativistic electrons, and why can they dominate in the corona? How do the compositions of accelerated and ambient material vary with space and time, and why?

The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) instrument, launched in 2002, provided the first combined imaging and high-resolution spectroscopy in the HXR/gamma-ray range. RHESSI's volumes of detailed study on electron-associated emission <1 MeV is in contrast to comparatively few ion-associated gamma-ray observations. Over the past two solar cycles RHESSI has imaged only five flares at the 2.2 MeV neutron-capture line and has been able to resolve ion lines in ~30 events. My research aims to expand this small set gamma-ray flare observations by (1) using new techniques to study flares obscured by high-background counts in the existing RHESSI dataset and (2) providing new observations through the development and flight of the Gamma-Ray Imager/Polarimeter for Solar Flares (GRIPS) instrument.

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