GRB 021004 modelled by multiple energy injections

GRB 021004 is one of the best sampled gamma-ray bursts (GRB) to date, although the nature of its light curve is still being debated. Here we present 107 new optical, near-infrared (NIR) and millimetre observations, ranging from 2 h to more than a year after the burst. Fitting the multiband data to a model based on multiple energy injections suggests that at least 7 refreshed shocks took place during the evolution of the afterglow, implying a total energy release (collimated within an angle of 1$\fdg$8) of ~$8 \times 10^{51}$ erg. Analysis of the late photometry reveals that the GRB 021004 host is a low extinction ($A_{\rm V}\sim0.1$) starburst galaxy with $M_{B}\simeq-22.0$.