A comparison between the spectral parameters of both electron and proton dominated events

Investigation of the gamma-ray spectra observed by the GRS/SMM leads to the conclusion that there exist two extreme cases: electron-dominated spectra and proton-dominated spectra. The observation of different spectra is determined by both the spectral hardness of non-thermal electrons and the number ratio of protons to electrons. Any viable acceleration mechanism should be able to explain these differences in accelerating electrons versus protons. This revised version was published online in July 2006 with corrections to the Cover Date.