On the self-acceleration of fireshell

The Fireshell in a Gamma-Ray Burst (GRB) has the most unique feature in the entire field of physics of self-accelerating from a Lorentz gamma factor equal to 1 all the way to 200-300. The hysics of this most extraordinary system is based on the continuous annihilation of electron-positron pairs in an optically thick e$^{+}$e$^{-}$ plasma. The physical reasons for this self-acceleration reanalyzed and the fireshell dynamics is compared with the ``fireball'' solution usually adopted in GRB literature.