Implications of the Measured Image Size for the Radio Afterglow of GRB 030329

Abstract

We use data on the image size of the radio afterglow of GRB 030329 to constrain the physical parameters of this explosion. Together with the observed broadband spectrum, this data overconstrains the physical parameters, thus enabling us to test different GRB jet models for consistency. We consider two extreme models for the lateral spreading of the jet: model 1, with relativistic expansion in the local rest frame, and model 2, with little lateral expansion as long as the jet is highly relativistic. We find that both models are consistent with the data for a uniform external medium, while for a stellar wind environment model 1