The X-ray, optical and radio evolution of the GRB 030329 afterglow and the associated SN2003dh

Extensive X-ray, optical and radio observations of the bright afterglow of the gamma-ray burst GRB 030329 are used to construct the multifrequency evolution the event. The data are fitted using the standard fireball shock model to provide estimates of the initial energy, epsilon = 6.8 x 10(52) erg sr(-1), the density of the ambient medium, n(0) = 1 cm(-3), the electron and magnetic energy density fractions, epsilon(e) = 0.24 and epsilon(B) = 0.0017, the power-law index of the relativistic electron spectrum, p = 2.25, and the opening angle of the jet, theta(j) = 3degrees. Deviations from the standard model seen in the optical and radio are most likely attributable to the concurrent hypernova SN2003dh. Peaks at 0.23 and 1.7 d in the R-band are much brighter than expected from a standard supernova (SN), and there is a large radio excess over the expected afterglow flux for t > 2 d. No deviation from the best-fitting afterglow model is seen in the X-ray decline, indicating that the excess optical and radio flux from 1-5 d arises from a later injection of slower electrons by the central engine.