  The complex multiwavelength emission of GRB afterglow 130427A (monitored in
the radio up to 10 days, in the optical and X-ray until 50 days, and at GeV
energies until 1 day) can be accounted for by a hybrid reverse-forward shock
synchrotron model, with inverse-Compton emerging only above a few GeV. The high
ratio of the early optical to late radio flux requires that the ambient medium
is a wind and that the forward-shock synchrotron spectrum peaks in the optical
at about 10 ks. The latter has two consequences: the wind must be very tenuous
and the optical emission before 10 ks must arise from the reverse-shock, as
suggested also by the bright optical flash that Raptor has monitored during the
prompt emission phase (<100 s). The VLA radio emission is from the
reverse-shock, the Swift X-ray emission is mostly from the forward-shock, but
the both shocks give comparable contributions to the Fermi GeV emission. The
weak wind implies a large blast-wave radius (8 t_{day}^{1/2} pc), which
requires a very tenuous circumstellar medium, suggesting that the massive
stellar progenitor of GRB 130427A resided in a super-bubble.
