X-ray and Gamma-ray Observations of Solar Flares with RHESSI

Sam Krucker

Solar flares are the most powerful explosions in our solar system,
releasing up to 1e32-1e33 ergs in ~10-1000 s. The flare-accelerated
~20-100 keV electrons (and sometimes >1 MeV/nucleon ions)
appear to contain a significant fraction, ~10-50 %, of this energy,
indicating that the particle acceleration and energy release processes
are intimately linked. Magnetic reconnection was originally proposed
to explain the rapid release of energy in solar flares.

X-ray and Gamma-ray observations are excellent diagnostics of
accelerated particles: Accelerated electrons colliding
with the ambient solar atmosphere produce bursts of bremsstrahlung
hard X-rays; and collisions of accelerated ions with the atmosphere
result in a complex spectrum of narrow and broad gamma-ray lines.
Here I summarize the latest result provided by the Reuven Ramaty High
Energy Solar Spectroscopic Imager (RHESSI) mission. This review
focuses on observational evidence for and against the importance of
magnetic reconnection in solar flares.