Astrophysics: refreshed shocks from a gamma-ray burst.

In addition to its remarkable supernova signature1,2, the γ-ray burst of 29 March 2003 (GRB030329) had two interesting peculiarities: an unusually low-energy output in γ-rays and a large bump in its afterglow light curve after 1–2 days (followed by several less significant rebrightening episodes). We suggest that refreshed shocks — slow shells ejected from the source that catch up with the afterglow shock a relatively long time after the initial burst — produced the observed fluctuations in the early afterglow light curve and explain the low-energy output at early times.