5 Discussion  

We have demonstrated for the first time that the electron and magnetic field energy densities are close to but somewhat below equipartition value. The ambient density is on the low side of normal for a disc of a galaxy but definitely higher than expected for a halo, lending support to the notion that bursts occur in gas-rich environments.

It is interesting to compare the properties at late times with those derived from radio observations. The scintillation size after 1 month is about 10¹⁷cm (Frail et al. 1997), whereas our formulae give a transverse size of $3\ 10^{17}$cm, in reasonable agreement given the statistical nature of the scintillation size and our neglect of the gradients in properties in the transverse direction. The Lorentz factor at this time is 3, so the evolution is still in the relativistic regime. The co-moving field at this time is $B^\prime=0.06$G.