2006/07/24 by Akira Mizuta, Tatsuya Yamasaki, Shigehiro Nagataki +1 · 2 citations
Physics and Astronomy · #Astrophysical Phenomena and Observations #Astrophysics #Astrophysics and Cosmic Phenomena #Classical mechanics #Collimated light #Gamma-ray burst #Gamma-ray bursts and supernovae #Jet (fluid) #Lorentz factor #Lorentz transformation #Mechanics #Meteorology #Optics #Outflow #Physics #RADIUS #Shock (circulatory) #Shock wave #astro-ph
paper · pdf · doi:10.1086/507861
published as Astrophys.J.651:960-978,2006 · Comments 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
arxiv created 2006/07/24 · openalex publication_date 2006/11/02 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We investigate the dynamics of an outflow propagating in a progenitor in the context of the collapsar model for 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 (10 51 ergs s -1 ) and radius of the injected outflow (7 × 10 7 cm) while varying its bulk Lorentz factor, Γ 0 = 1.05-5, and its specific internal energy, 0 / c 2 = 0.1-30 (with c being speed of light). We find a smooth but dramatic transition from a collimated jet to an expanding outflow among calculated models. The half opening angle of the outflow (θ sim ) is sensitive to Γ 0 ; we find θ sim < 2 ° for Γ 0 ≳ 3. The maximum Lorentz factor is, on the other hand, sensitive to both Γ 0 and 0 : roughly Γ max ~ Γ 0 (1 + 0 / c 2 ). In particular, a very high Lorentz factor of Γ max ≳ 100 is achieved in one model. A variety of opening angles can arise by changing 0 , even when the maximum Lorentz factor is fixed. The jet structure totally depends on Γ 0 . When Γ 0 is high, high-pressure progenitor gas heated by the bow shock collimates the outflow to form a narrow, relativistic jet. When Γ 0 is low, on the contrary, the outflow expands soon after the injection, since the bow shock is weak and thus the pressure of the progenitor gas is not high enough to confine the flow. 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 0 values.