Akira Mizuta, Kunihito Ioka
We investigate the jet propagation and breakout from the stellar progenitor for gamma-ray burst (GRB) collapsars by performing 2D relativistic hydrodynamic simulations with analytical analyses. We find that the jet opening angle is given by $\theta_j \sim 1/5 \Gamma_{0}$, and infer the initial Lorentz factor of the jet at the central engine $\Gamma_0$ about a few for observations. The jet keeps the Lorentz factor inside the star by converging cylindrically via collimation shocks under the cocoon pressure, and makes a jet-breakout acceleration before the free expansion to a hollow-cone structure with a sharp edge. Some bursts violating the maximum opening angle $\theta_{j,\max}\sim 1/5 \sim 12^{\circ}$ imply a two-component jet. We explain both the Amati and Yonetoku spectral relations only with one assumption in the off-center photosphere model. We also numerically calibrate the pre-breakout model (Bromberg et al. 2011) for later use.
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http://arxiv.org/abs/1304.0163
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