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(Shortened) The Swift and HETE-2 discovery of an afterglow associatedpossibly with short GRBs opened the new problematic of their nature andclassification. This has been further enhanced by the GRB060614 observation andby a re-analysis of the BATSE catalog leading to the identification of a newGRB class with "an occasional softer extended emission lasting tenths ofseconds after an initial spikelike emission". We plan: a) to fit this new classof "hybrid" sources within our "canonical GRB" scenario, where all GRBs aregenerated by a "common engine" (i.e. the gravitational collapse to a blackhole); b) to propose GRB970228 as the prototype of the such a class. We analyzeBeppoSAX data on GRB970228 in the 40-700 keV and 2-26 keV energy bands withinthe "fireshell" model. We find that GRB970228 is a "canonical GRB", like e.g.GRB050315, with the main peculiarity of a particularly low CircumBurst Medium(CBM) average density n_{cbm}~10^{-3} #/cm^3. We also simulate the light curvecorresponding to a rescaled CBM density profile with n_{cbm}=1 #/cm^3. Fromsuch a comparison it follows that the total time-integrated luminosity is afaithful indicator of the GRB nature, contrary to the peak luminosity which ismerely a function of the CBM density. We call attention on discriminating theshort GRBs between the "genuine" and the "fake" ones. The "genuine" ones areintrinsically short, with baryon loading B \la 10^{-5}, as stated in ouroriginal classification. The "fake" ones, characterized by an initial spikelikeemission followed by an extended emission lasting tenths of seconds, have abaryon loading 10^{-4} \la B \leq 10^{-2}. They are observed as such only dueto an underdense CBM consistent with a galactic halo environment which deflatesthe afterglow intensity.

GRB970228 and a class of GRBs with an initial spikelike emission