  The "Supercritical Pile" is a very economical GRB model that provides for the
efficient conversion of the energy stored in the protons of a Relativistic
Blast Wave (RBW) into radiation and at the same time produces - in the prompt
GRB phase, even in the absence of any particle acceleration - a spectral peak
at energy $\sim 1$ MeV. We extend this model to include the evolution of the
RBW Lorentz factor $\Gamma$ and thus follow its spectral and temporal features
into the early GRB afterglow stage. One of the novel features of the present
treatment is the inclusion of the feedback of the GRB produced radiation on the
evolution of $\Gamma$ with radius. This feedback and the presence of kinematic
and dynamic thresholds in the model are sources of potentially very rich time
evolution which we have began to explore. In particular, one can this way
obtain afterglow light curves with steep decays followed by the more
conventional flatter afterglow slopes, while at the same time preserving the
desirable features of the model, i.e. the well defined relativistic electron
source and radiative processes that produce the proper peak in the $\nu
F_{\nu}$ spectra. In this note we present the results of a specific set of
parameters of this model with emphasis on the multiwavelength prompt emission
and transition to the early afterglow.
