  The death of massive stars produces a variety of supernovae, which are linked
to the structure of the exploding stars. The detection of several precursor
stars of Type II supernovae have been reported, however we do not yet have
direct information on the progenitors of the hydrogen deficient Type Ib and Ic
supernovae. Here we report that the peculiar Type Ib supernova SN2006jc is
spatially coincident with a bright optical transient that occurred in 2004.
Spectroscopic and photometric monitoring of the supernova leads us to suggest
that the progenitor was a carbon-oxygen Wolf-Rayet star embedded within a
helium-rich circumstellar medium. There are different possible explanations for
this pre-explosion transient. It appears similar to the giant outbursts of
Luminous Blue Variables (LBV) of 60-100 solar mass stars, however the
progenitor of SN2006jc was helium and hydrogen deficient. An LBV-like outburst
of a Wolf-Rayet star could be invoked, but this would be the first
observational evidence of such a phenomenon. Alternatively a massive binary
system composed of an LBV which erupted in 2004, and a Wolf-Rayet star
exploding as SN2006jc, could explain the observations.
