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We studied the evolution of two small flares (GOES class C2 and C1) thatdeveloped in the same active region with different morphologicalcharacteristics: one is extended and the other is compact. We analyzed theaccuracy and the consistency of different algorithms implemented in RHESSIsoftware to reconstruct the image of the emitting sources, for energies between3 and 12 keV. We found that all tested algorithms give consistent results forthe peak position whil the other parameters can differ at most by a factor 2.Pixon and Forward-fit generally converge to similar results but Pixon is morereliable for reconstructing a complex source. We investigated the spectralcharacteristics of the two flares during their evolution in the 3--25 keVenergy band. We found that a single thermal model of the photon spectrum isinadequate to fit the observations and we needed to add either a non-thermalmodel or a hot thermal one.The non-thermal and the double thermal fits arecomparable. If we assume a non-thermal model, the non-thermal energy is alwayshigher than the thermal one.Only during the very final decay phase a singlethermal model fits fairly well the observed spectrum.Comment: 26 pages, 11 figures, accepted by Solar Physic

Rhessi Images and Spectra of Two Small Flares