Type Ib/c supernovae observations with VLBI

Supernovae (SNe) Ib/c have drawn increasing attention since 1998 owing to their sparse association with long duration gamma-ray bursts (GRBs). Although both phenomena originate from the core collapse of a massive star, the former release most of their energy at optical wavelengths, while the latter do it mostly in soft gamma-rays or hard X-rays. Moreover, the GRB central engine generates ultra-relativistic jets, which beam the early emission into a small narrow cone; no relativistic outflows have yet been found in SNe Ib/c explosions. We show results from very long baseline interferometry (VLBI) observations of three supernovae, one of which appears to have produced a collimated, mildly relativistic outflow.