With the discovery of Type Ic SNe 1998bw and 2006aj in association with nearby GRB 980425 and XRF 060218, respectively, a new class of cosmic explosion has been identified. In comparison with typical GRBs, these events are sub-energtic by a factor of 100 but are up to 10 times more common. Moreover, they are distinguished from ordinary Type Ibc supernovae by the presense of a central engine.
... [Show full abstract] These intermediate explosions are identified through radio observations which probe relativistic material. Motivated by SN 1998bw, we began a comprehensive study of local Type Ibc SNe with the Very Large Array in 1999. Since then we have observed 150 optically-selected local (d < 150 Mpc) SNe Ibc, each within a few weeks of explosion. This six-year effort has resulted in two key advances. The first is a clear distinction between GRBs/XRFs and ordinary SNe Ibc: engine-driven explosions are rare, less than 3% of the local sample, and couple at least 10^{48} erg to mildly-relativistic ejecta. Second, we find a wide dispersion in the radio properties of SNe Ibc, implying significant variations in their ejecta properties, environments and/or progenitor systems. I will discuss the surprising results of our ongoing survey and the complex picture of stellar death that is emerging.