  Here we report the discovery in the X-ray band of the first afterglow of a
gamma-ray burst. It was detected and quickly positioned by the Beppo-SAX
satellite on 1997 February 28 (GRB970228). The X-ray afterglow source was
detected with the X-ray telescopes aboard the same satellite about eight hours
after the burst and faded away in a few days with a power law decay function.
The energetic content of the X-ray afterglow results to be a significant
fraction of gamma-ray burst energetics. The Beppo-SAX detection and fast
imaging of GRB970228 started a multiwavelength campaign that lead to the
identification of a fading optical source in a position consistent with the
X-ray source.
