According the Collapsar model long GRBs (LGRBs) arise during the collapse of 
a massive star and involve the emergence of a relativistic jet through the envelope
of the exploding star.
This model naturally explains the links between LGRBs and SNe, such as the
the association of half a dozen LGRBs with broad-line Ic SNe.
However, a closer look at this association reveals that four out of the six
bursts differ form ordinary LGRBs:
They are less luminous, have a smooth lighcurve and their spectra show
no evident for a high energy tail.
The nature of these low luminosity GRBs is puzzling, and it is
interesting to see whether they originate in the same way as LGRBs.
We examine the propagation of a relativistic jet inside a stellar envelope,
and find that the jets involved in low luminosity GRBs are not powerful enough to
break out of their progenitors.
This implies that their gamma-ray emission must be generated by a different mechanism
than that of luminous LGRBs.
The high rate of the low luminosity GRBs indicates that jets
that are generated following a core collapse,
have a higher chance of being buried rather than  breaking out.
This puts the GRB-SN connection in a new light where
typical SNe engines can only generate low luminosity GRBs while only the most
powerful ones can generate  LGRBs.