  Many stripped envelope supernovae (SNe) present a signature of high-velocity
material responsible for broad absorption lines in the observed spectrum. These
include SNe that are associated with long gamma-ray bursts (LGRBs) and
low-luminosity GRBs (llGRBs), and SNe that are not associated with GRBs.
Recently it was suggested that this high velocity material originates from a
cocoon that is driven by a relativistic jet. In LGRBs this jet breaks out
successfully from the stellar envelope, while in llGRBs and SNe that are not
associated with GRBs the jet is choked. Here we use numerical simulations to
explore the velocity distribution of an outflow that is driven by a choked jet
and its dependence on the jet and progenitor properties. We find that in all
cases where the jet is not choked too deep within the star, the outflow carries
a roughly constant amount of energy per logarithmic scale of proper velocity
over a wide range of velocities, which depends mostly on the cocoon volume at
the time of its breakout. This is a universal property of jets driven outflows,
which does not exist in outflows of spherically symmetric explosions or when
the jets are choked very deep within the star. We therefore conclude that jets
that are choked (not too deep) provide a natural explanation to the fast
material seen in the early spectra of stripped envelope SNe that are not
associated with LGRBs and that properties of this material could reveal
information on the otherwise hidden jets.

High Energy Astrophysical Phenomena