New two- and three-dimensional calculations are presented of relativistic jet propagation and break out in massive Wolf-Rayet stars .
Such jets are thought responsible for gamma-ray bursts .
As it erupts , the highly relativistic jet core ( 3 to 5 degrees ; \Gamma \gtrsim 100 ) is surrounded by a cocoon of less energetic , but still moderately relativistic ejecta ( \Gamma \sim 15 ) that expands and becomes visible at larger polar angles ( \sim 10 degrees ) .
These less energetic ejecta may be the origin of X-ray flashes and other high-energy transients which will be visible to a larger fraction of the sky , albeit to a shorter distance than common gamma-ray bursts .
Jet stability is also examined in three-dimensional calculations .
If the jet changes angle by more than three degrees in several seconds , it will dissipate , producing a broad beam with inadequate Lorentz factor to make a common gamma-ray burst .
This may be an alternate way to make X-ray flashes .