jet cocoon

Noun

 * 1)  A cloud of gas that obscures the poles of a star undergoing hypernova (HN), which gets heated by the polar jet escaping the hypernova progenitor star (hnp), and may absorb the energy of a weak gamma-ray burst (GRB), leaving an observable HN lacking the associated GRB, or be penetrated by a stronger GRB, giving a HN with an associated GRB.