  We report high-energy spectral data of the prompt emission of GRB970228 and
its X-ray afterglow. We establish that the nature of the X-ray afterglow
emission is non-thermal and similar to the later portion of GRB970228. Our data
can be used to discriminate different emission models of GRB afterglows. While
cooling of excited compact objects can be ruled out, fireball models are
constrained in the physics of the radiation emission processes and their
evolution.
