  Radio observations of Type Ib/c supernovae suggest that circumstellar
interaction takes place with a wide range of wind densities, comparable to that
seen in Galactic Wolf-Rayet stars. Efficient production of magnetic field in
the shocked region is needed. The X-ray emission observed from some Type Ib/c
supernovae is higher than would be expected by the thermal or inverse Compton
mechanisms; a synchrotron interpretation requires a flattening of the electron
energy spectrum at high energies, as might occur in a cosmic ray dominated
shock wave. The wind density variations that are indicated in two supernovae
may be due to a binary companion, although variable mass loss from a single
star remains a possibility. Other than the optical supernova radiation, the
emission from the nearby SN 2006aj/GRB 060218 appears to be powered by a
central engine, while that from SN 1998bw/GRB 980425 could be powered by either
a central engine or the outer supernova ejecta.
