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

Abstract

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, ɛ= 6.8 × 10⁵² erg sr^-1, the density of the ambient medium, n₀= 1 cm^-3, the electron and magnetic energy density fractions, ɛ_e= 0.24 and ɛ_B= 0.0017, the power-law index of the relativistic electron spectrum, p= 2.25, and the opening angle of the jet, θ_j= 3°. 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.