RHESSI Gamma-ray/Hard X-ray Imaging Spectroscopy Observations of Particle Acceleration in Solar Flares R. P. Lin , Professor of Physics, Physics Department & Space Sciences Laboratory, University of California, Berkeley, California

The Sun is the most energetic particle accelerator in the solar system, producing ions up to 10s of GeV and electrons to 100s of MeV, in both large solar flares and fast coronal mass ejections (CMEs), but through different physical mechanisms. Solar flares are the most powerful explosions in the solar system, releasing up to 1032-1033 ergs in 100-1000 s, most likely through magnetic reconnection, with up to ~10-50% of this energy in accelerated electrons and ions. The intense solar energetic particle (SEP) events observed in the interplanetary medium, however, appear to be accelerated by shock waves driven by fast CMEs. The RHESSI (Ramaty High Resolution Solar Spectroscopic Imager) mission launched in 2002 provides a new window on particle acceleration at the Sun, through imaging spectroscopy of the hard X-ray (HXR)/gamma-ray continuum and gamma-ray line emission produced by the accelerated electrons and ions, respectively. I will present results from RHESSI, including the first imaging of solar energetic ions at the Sun, the first high-resolution gamma-ray line spectroscopy and HXR imaging spectroscopy of solar flares. I will discuss the implications for our understanding of the flare energy release and particle acceleration processes, and of the relationship of flare particle acceleration to SEPs observed near 1 AU.