  Over the past decade our physical understanding of gamma-ray bursts (GRBs)
has progressed rapidly thanks to the discovery and observation of their
long-lived afterglow emission. Long-duration (T < 2 s) GRBs are associated with
the explosive deaths of massive stars (``collapsars''), which produce
accompanying supernovae, while the short-duration (T > 2 s) GRBs arise from a
different origin, which has been argued to be the merger of two compact
objects, either neutron stars or black holes. Here we present observations of
GRB060614, a 100-s long burst discovered by the Swift satellite, which require
the invocation of a new explosive process: either a massive ``collapsar'' that
powers a GRB without any associated supernova, or a new type of engine, as
long-lived as the collapsar but without any such massive stellar host. We also
discuss the properties of this burst's redshift z=0.125 host galaxy, which
distinguish it from other long-duration GRBs and suggest that an entirely new
type of GRB progenitor may be required.
