  We report the discovery and monitoring of radio emission from the Type Ic SN
2002ap ranging in frequency from 1.43 to 22.5 GHz, and in time from 4 to 50
days after the SN explosion. As in most other radio SNe, the radio spectrum of
SN 2002ap shows evidence for absorption at low frequencies, usually attributed
to synchrotron self-absorption or free-free absorption. While it is difficult
to discriminate between these two processes based on a goodness-of-fit, the
unabsorbed emission in the free-free model requires an unreasonably large
ejecta energy. Therefore, on physical grounds we favor the synchrotron
self-absorption (SSA) model. In the SSA framework, at about day 2, the shock
speed is approximately 0.3c, the energy in relativistic electrons and magnetic
fields is approximately 1.5e45 erg and the inferred progenitor mass loss rate
is approximately 5e-7 solar masses per year (assuming a 1,000 km/sec wind).
These properties are consistent with a model in which the outer, high velocity
supernova ejecta interact with the progenitor wind. The amount of relativistic
ejecta in this model is small, so that the presence of broad lines in the
spectrum of a Type Ib/c supernova, as observed in SN 2002ap, is not a reliable
indicator of a connection to relativistic ejecta and hence gamma-ray emission.
