This project is the continuation of a previous one (with title The RHESSI Mission: X-Ray Spectra and Image Analysis by Means of Inversion Methods), funded by ISSI for the period 2005-2006. That project was devoted to the formulation of inverse methods for the analysis of solar X-ray data recorded by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), launched by NASA on February 5, 2002. Among the results obtained so far are the development of models and methods for the analysis of photon spectra [1,2,3,7,8,14,15] and the implementation of an IDL code for inference of source electron spectra from hard X-ray spectra. This code has been modified to enable it to be used by the scientific community and it is being integrated into the official RHESSI software.

The main goal of the proposed project is to integrate 2D spatial imaging in hard X-rays and gamma rays with 1D high resolution spectroscopy into an imaging-spectroscopy approach which will allow spectral changes associated with the propagation of the emitting electrons to be measured and assessed against candidate energy transport models. The main objectives of the project are:

1) to incorporate a priori knowledges of the spectral shapes into the image reconstruction methods;

2) to determine the image properties (size, shape, location, orientation) as a function of energy by means of a forward-fitting approach using visibility;

3) to model the imaging-spectroscopy approach as a three-dimensional linear inverse problem characterized by one spectral and two spatial dimensions and to formulate a regularization-based inverse method for its solution.

Such imaging spectroscopy approach represents an important new capability not previously available in this wavelength range that will provide powerful new constraints on the mechanisms of energy gain and loss during solar flares.