Collimated Jet or Expanding Outflow: Possible Origins of GRBs and X-Ray Flashes

Akira Mizuta; Tatsuya Yamasaki; Shigehiro Nagataki; Shin Mineshige

doi:10.1086/507861

paper

Collimated Jet or Expanding Outflow: Possible Origins of GRBs and X-Ray Flashes

arXiv:astro-ph/0607544 · doi:10.1086/507861

Abstract

We investigate the dynamics of an injected outflow propagating in a progenitor in the context of the collapsar model for gamma-ray bursts (GRBs) through two dimensional axisymmetric relativistic hydrodynamic simulations. Initially, we locally inject an outflow near the center of a progenitor. We calculate 25 models, in total, by fixing its total input energy to be 10^{51} ergs s^{-1} and radius of the injected outflow to be $7 \times 1 0^{7}$ cm while varying its bulk Lorentz factor, $Γ_{0} = 1.05 \sim 5$ , and its specific internal energy, $ε_{0} / c^{2} = 0.1 \sim 30$ . The injected outflow propagates in the progenitor and drives a large-scale outflow or jet. We find a smooth but dramatic transition from a collimated jet to an expanding outflow among calculated models. The maximum Lorentz factor is, on the other hand, sensitive to both of $Γ_{0}$ and $ε_{0}$ ; roughly $Γ_{max} \sim Γ_{0} (1 + ε_{0} / c^{2})$ . Our finding will explain a smooth transition between the GRBs, X-ray rich GRBs (XRRs) and X-ray Flashes (XRFs) by the same model but with different $ε_{0}$ values.

arXiv commentComments 51 pages, 21 figures. accepted for publication in ApJ high resolution version is available at http://www.mpa-garching.mpg.de/~mizuta/COLLAPSAR/collapsar.html

Collimated Jet or Expanding Outflow: Possible Origins of GRBs and X-Ray Flashes

Abstract

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