INTRODUCTION

Observations of solar flares are very important tools of studying magnetic reconnection, particle acceleration and other plasma processes, the result of which can have significant implications for other astrophysical phenomena. Observations by low spectral and spatial resolution instruments can give us only the lightcurve and a crude spectrum of the whole flare which may consist of many distinct sources with different characteristics. One of the significant advancement achieved by the YOHKOH satellite is the discovery of distinct looptop (LT) sources in addition to the normal footpoint (FP) sources (Sakao et al. 1994; Masuda et al. 1994). These new observations provide further evidence for stochastic acceleration model (Petrosian et al. 1999, 2002), which was shown to be consistent with the broadband spectra of several solar flares (Park et al. 1997). As suggested by this and other models, these different sources should have different electron distributions and spectra determined by the physical condition at the acceleration site. RHESSI with its unprecedented spectral and spatial resolutions can image at different energy bands. This exceptional imaging spectroscopic capacity, combined with its excellent time resolution, provides us a multi-dimensional pictures of solar flares, which can set stringent constraints on the model parameters and will eventually improve our understanding of the relevant physical processes.

Several bright flares observed by RHESSI have been extensively analyzed in this respect, demonstrating its capabilities. In this paper, we present results from our study of 22 limb flares. We describe the flare selection criteria, the imaging procedure. The advantages and/or weaknesses of different software packages are also discussed. In this paper, we focus on the imaging and lightcurves of the LT and FP sources. The spectra of the sources are presented in a complementary paper (Jiang et al,; poster # 18.03).