Radio and X-Ray Diagnostics of Energy Release in Solar Flares

Solar flares involve catastrophic release of magnetic energy previously stored in the Sun's corona. This dissertation focuses on studies of radio and X-ray emissions as diagnostics of energy release processes in flares and the environment in which they occur.

A major part of the dissertation is exploiting spatially resolved dynamic spectroscopy to study coherent radio bursts. The Frequency-Agile Solar Radiotelescope Subsystem Testbed, a three-element radio interferometer, provides the first opportunity of doing such studies on zebra-pattern bursts. The observations allow us to identify the relevant emission mechanism, enabling diagnostics of the plasma parameters in the source. With the help of coronal magnetic field extrapolations, the source is placed into a three-dimensional magnetic field configuration and its relation to the energy release is clarified. The next part of the dissertation discusses the "solar mode" commissioning of the recently upgraded Karl G. Jansky Very Large Array (VLA). As a general purpose telescope, special provisions should be made for the VLA to enable solar observations. Based on the test results on the VLA's hardware, solar observing and calibration strategies are developed. Now the VLA serves as the most powerful radio telescope currently available for solar observing, capable of performing simultaneous imaging and dynamic spectroscopy over a large bandwidth at high spatial, spectral, and temporal resolution. The upgraded VLA is used to observe decimetric type III radio bursts, which are the radio signature of propagating fast electron beams produced in flares. The new observing technique allows detailed trajectories of these electron beams to be derived. Combined with multi-wavelength observations, the properties of the energy release site, electron beams, and the surrounding coronal medium are deduced.

The dissertation also presents a study on coronal hard X-ray/gamma-ray sources. Rather extreme conditions are needed to account for some observed coronal hard X-ray/gamma-ray sources using the usually-assumed non-thermal bremsstrahlung emission. This study investigates whether inverse Compton scattering could be an alternative emission mechanism for these sources, which would open a new window in diagnosing the flare energy release.