A Unified Treatment of the Gamma-Ray Burst 021211 and Its Afterglow Emissions

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 ǫB , to be larger than the forward shock at 11 minutes by a factor of about 103. 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 ǫB in forward shock at deceleration to be larger than the value at 11 minutes by a factor of about 102. 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. Subject headings: gamma-rays: bursts, theory, methods: analytical – radiation mechanisms: non-thermal shock waves