  Gamma-ray bursts are often the brightest objects in the sky during their
short life. Particle acceleration in trans-relativistic shocks, internal to the
main blastwave, may explain the early intensity peaks, and particle
acceleration in the main blastwave, as it slows from ultrarelativistic speeds
to the trans-relativistic range, may explain the afterglow. If the radiation
results from energetic leptons, how do leptons become energized? A nonlinear
relativistic Monte Carlo model was developed and used to study lepton and
baryon acceleration by parallel shocks in the trans-relativistic range. Given
the assumptions of this model, if the lepton and baryon number densities are of
the same order, leptons will always carry far less energy than baryons.
However, if the lepton density exceeds the baryon density by a factor of
300,000, the shock is modified primarily by leptons and energy equipartition
between leptons and baryons occurs. The lepton to baryon number density ratio
for energy equipartition is independent of shock speed over the
trans-relativistic range of Lorentz factors used in this study.
