  We study the relativistically expanding electron-positron pair plasma formed
by the process of vacuum polarization around an electromagnetic black hole
(EMBH). Such processes can occur for EMBH's with mass all the way up to $6\cdot
10^5M_\odot$. Beginning with a idealized model of a Reissner-Nordstrom EMBH
with charge to mass ratio $\xi=0.1$, numerical hydrodynamic calculations are
made to model the expansion of the pair-electromagnetic pulse (PEM pulse) to
the point that the system is transparent to photons. Three idealized special
relativistic models have been compared and contrasted with the results of the
numerically integrated general relativistic hydrodynamic equations. One of the
three models has been validated: a PEM pulse of constant thickness in the
laboratory frame is shown to be in excellent agreement with results of the
general relativistic hydrodynamic code. It is remarkable that this precise
model, starting from the fundamental parameters of the EMBH, leads uniquely to
the explicit evaluation of the parameters of the PEM pulse, including the
energy spectrum and the astrophysically unprecedented large Lorentz factors (up
to $6\cdot 10^3$ for a $10^3 M_{\odot}$ EMBH). The observed photon energy at
the peak of the photon spectrum at the moment of photon decoupling is shown to
range from 0.1 MeV to 4 MeV as a function of the EMBH mass. Correspondingly the
total energy in photons is in the range of $10^{52}$ to $10^{54}$ ergs,
consistent with observed gamma-ray bursts. In these computations we neglect the
presence of baryonic matter which will be the subject of forthcoming
publications.

Astrophysics