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 \approx 0.3 c , the energy in relativistic electrons and magnetic fields is \approx 1.5 \times 10 ^ { 45 } erg and the inferred progenitor mass loss rate is \approx 5 \times 10 ^ { -7 } M _ { \odot } /yr ( assuming a 10 ^ { 3 } km sec ^ { -1 } 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 .