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 jet is surrounded by a cocoon of less energetic, but still highly relativistic ejecta that expands and becomes visible at much larger polar angles. 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.
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