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 ^ { 5 } M _ { \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 .