Gamma-ray spectroscopy of the 2003 October 29 solar flare using RHESSI imaging

The solar system's most powerful explosions occur at the Sun, capable of releasing up to 10^33 ergs. The most powerful of these explosions release high-energy gamma rays and hard X-rays which encode key information about particle acceleration as well as the ambient solar environment. Here we present a study of one of the largest solar flares (GOES class X10) to have been captured by the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) instrument, occurring on October 29, 2003. This flare had previously been obscured by high background counts due to the magnetospheric response of another large flare that occurred the previous day. In this study, we use a Fourier-imaging technique to eliminate background before performing spectroscopy using the imaged flux. RHESSI's bi-collimated grid design phase modulates incoming solar photons before they are collected by the spectrometer. A back-projection technique is used to reconstruct an image from knowledge of grid orientation and detector counts. Since background counts are not phase modulated, they are generally insignificant in the back-projected image's derived flux. In this study we present spectra from the October 29 event, place this event in context with other large flares by adding this event to the correlation plots from Shih et al. (2009) and examine the limitations of this method.