The Radio Evolution of the Ordinary Type I[CLC]c[/CLC] Supernova SN 2002[CLC]ap[/CLC]

We report the discovery and monitoring of radio emission from the Type Ic SN2002ap ranging in frequency from 1.43 to 22.5 GHz, and in time from 4 to 50days after the SN explosion. As in most other radio SNe, the radio spectrum ofSN 2002ap shows evidence for absorption at low frequencies, usually attributedto synchrotron self-absorption or free-free absorption. While it is difficultto discriminate between these two processes based on a goodness-of-fit, theunabsorbed emission in the free-free model requires an unreasonably largeejecta energy. Therefore, on physical grounds we favor the synchrotronself-absorption (SSA) model. In the SSA framework, at about day 2, the shockspeed is approximately 0.3c, the energy in relativistic electrons and magneticfields is approximately 1.5e45 erg and the inferred progenitor mass loss rateis 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 velocitysupernova ejecta interact with the progenitor wind. The amount of relativisticejecta in this model is small, so that the presence of broad lines in thespectrum of a Type Ib/c supernova, as observed in SN 2002ap, is not a reliableindicator of a connection to relativistic ejecta and hence gamma-ray emission.Comment: Submitted to ApJL; 7 pages, 1 table, 2 figure