SPRG Seminars
September 20, 2011:
" Solar flares, accelerated ions, and the upcoming GRIPS instrument "
Albert Shih, NASA/GSFC
A large fraction (up to tens of percent) of the energy released in solar flares goes into accelerated ions and electrons, and these two populations can have comparable energy content. RHESSI observations have shown a striking close linear correlation of gamma-ray line fluence from accelerated ions >~20 MeV and bremsstrahlung emission from relativistic accelerated electrons >300 keV, suggesting a common acceleration mechanism. The correlation worsens when considering electrons at lower energies, suggesting that electrons below 300 keV may also be accelerated by other processes. We investigate the possibility of two classes of flares with high-energy acceleration. We also use the latest RHESSI gamma-ray analysis techniques to study the temporal behavior of the larger RHESSI flares, and determine what changes can be attributed to an evolving acceleration mechanism or to evolving abundances, either in the ambient or accelerated populations. Finally, I will discuss the latest progress in building the Gamma-Ray Imager/Polarimeter for Solar flares (GRIPS), a balloon-based instrument that will produce gamma-ray images with an unparalleled angular resolution of 12.5 arcseconds, and the science questions GRIPS will address.