The PI plans to use solar flare spectral data obtained with the Ramaty High Energy Solar Spectroscopic Imager (RHESSI) to determine the cause of the observed double power-law hard X-ray spectrum. Because both particle acceleration and transport processes are involved when particles radiate hard X-rays, it is unclear at present whether the double power-law is caused by the acceleration mechanism or by the transport process. The PI will test the two main mechanisms which could be responsible for the double power-law spectra, namely, the photospheric albedo effect and the beam return current effect. The contributions of these mechanisms are dependent on solar flare parameters, such as flare location, loop compactness, and beam flux strength.
Among other broader impacts, this study will place more constraints on the modeling of particle acceleration, and eventually identify the acceleration mechanism which is consistent with the obtained energy spectrum of accelerated electrons seen in RHESSI data. This study also has implications for energetic particle acceleration in general.
