The specific incidence of radio flares appears to be significantly largerthan that of the prompt optical emission. This abundance, coupled with thereverse shock interpretation suggests that radio flares add a unique probe onthe physics of GRB shocks. Motivated thus, we estimate the strength of thereverse shock expected for bursts in which multi-wavelength observations haveallowed the physical parameters of the forward shock to be determined. We useall 6 bursts (980519, 990123, 990510, 991208, 991216, 000418) which are foundto be adiabatic and thus predicted to have a strong reverse shock. We aim toconstrain the hydrodynamic evolution of the reverse shock and the initial bulkLorentz factor -- which we found to be between $10^{2}$ and $10^{3}$ and wellabove the lower limits derived from the requirement that gamma-ray bursts beoptically thin to high-energy photons. In half of the cases we improve thedescription of the early afterglow lightcurves by adding a contribution fromthe reverse shock. Modelling of this early emission provides the opportunity toinvestigate the immediate surroundings of the burst. For 991216 and 991208, theexpected $1/r^2$ density structure for a stellar wind is not compatible withthe early afterglow lightcurves. Considering the radial range relevant to theseGRBs, we discuss the conditions under which the inclusion of a wind terminationshock may resolve the absence of a $1/r^2$ density profile.
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