The Breakout of Relativistic Jets from Massive Wolf-rayet Stars

New twoand 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) 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 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. Subject headings: gamma rays: bursts—hydrodynamics—methods: numerical— relativity