2004ApJ...608..365Z

New two- and three-dimensional calculations are presented of relativistic jet propagation and break out in massive Wolf-Rayet stars. Such jets are thought to be responsible for gamma-ray bursts. As it erupts, the highly relativistic jet core (3° to 5°; Γ≳100) is surrounded by a cocoon of less energetic, but still moderately relativistic ejecta (Γ∼15) that expands and becomes visible at larger polar angles (∼10°). 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 3° 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.