  The Gamma-Ray Burst (GRB) 021211 detected by the High Energy Transient
Explorer (HETE) II had a simple light-curve in the x-ray and gamma-ray energy
bands containing one peak and little temporal fluctuation other than the
expected Poisson variation. Such a burst offers the best chance for a unified
understanding of the gamma-ray burst and afterglow emissions. We provide a
detailed modeling of the observed radiation from GRB 021211 both during the
burst and the afterglow phase. The consistency between early optical emission
(prior to 11 minutes), which presumably comes from reverse shock heating of the
ejecta, and late afterglow emission from forward shock (later than 11 minutes)
requires the energy density in the magnetic field in the ejecta, expressed as
fraction of the equipartition value or $\epsilon_B$, to be larger than the
forward shock at 11 minutes by a factor of about 10$^3$. We find that the only
consistent model for the gamma-ray emission in GRB 021211 is the synchrotron
radiation in the forward shock; to explain the peak flux during the GRB
requires $\epsilon_B$ in forward shock at deceleration to be larger than the
value at 11 minutes by a factor of about 10$^2$.
  These results suggest that the magnetic field in the reverse shock and early
forward shock is most likely frozen-in-field from the explosion, and therefore
a large fraction of the energy in the explosion was initially stored in
magnetic field. We can rule out the possibility that the ejecta from the burst
for GRB 021211 contained more than 10 electron-positron pairs per proton.
