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Gamma-Ray Burst Jets: dynamics and interaction with the progenitor star Davide Lazzati, Brian Morsony, and Mitch Begelman JILA - University of Colorado Davide Lazzati, Brian Morsony, and Mitch Begelman JILA - University of Colorado
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Evidence for SN association SN2003dh Stanek et al. 2003 Hjorth et al. 2003 SN1998bw Galama et al. 1998
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Phases of jet propagation Confined Jet Shock breakout Shocked jet Unshocked jet
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I: confined jet Jet head propagates under ram pressure equilibrium No mixing between shocked jet and star material Cocoon is over-pressured and drives shock into stellar material. Shock expands under Kompaneets approximation v sh ~(p cocoon / star ) 1/2. Cocoon cools adiabatically (relativistic EOS). Jet reacts to cocoon pressure with internal and ram pressure terms. Acceleration ~p -1/4. Lazzati & Begelman 2005
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I: confined jet In a monolithic jet the pressure scales with working surface P~ -1/2 Simulations show the monolithic approximation to be inaccurate. A boundary layer develops. Jet free inside, the velocity is parallel to the boundary in the layer z rr
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II: Shock breakout Is the first radiative phase: hot non- relativistic material is released on the stellar surface Ramirez-Ruiz et al. 2002 MacFadyen et al. 1999 Zhang et al. 2003
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III: Shocked Jet The jet in this phase is heavily affected by the transversal collimation shocks.
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IV: Unshocked Jet The evolution can be computed analogously to the confined jet geometry but now the cocoon pressure decreases with time. The opening angle of the jet grows with time
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Analytic vs. Numeric
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Cocoon pressure and breakout time are very well reproduced. Jet opening angle works better for jet initially out of causal contact (due to hyper- relativistic approximations). Energy stored in the cocoon: 8x10 50 vs. 9x10 50
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Analytic Results The break-out opening angle is smaller for more massive and large stars A jet with initial opening angle of 10 o and =10 is propagated through polytropic stars of varying mass and radius. WRPopIII
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Analytic Results A jet with initial opening angle of 10 o and =10 is propagated through polytropic stars of varying mass and radius. WRPopIII The break-out time depends very mildly on the mass, so too the energy deposited into the star
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Analytic Results Assuming =0.3 is a good approximation in most cases. As a consequence massive compact stars will NOT explode due to the jet propagation GRBs without SN? Exploding Stars Non exploding (no SN?)
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Numerical : movies
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Numerical Results
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Different observers see GRBs dominated by a different phase Small angles are dominated by shocked jet. Intermediate angles are dominated by unshocked jet Large angles are dominated by cocoon
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Numerical Results Precursor Dead times X-ray flash
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Summary A simple pressure balance explains some features of the jet/cocoon/star interaction and allows quantitative computations Jet can propagate fast in very massive stars if compact ( ~0.3 robust). PopIII GRBs? Jet propagation takes place in 4 phases: 3 radiative Cocoon = Precursor but we do not see shocked or un-shocked jet. Different observers are however dominated by different phases. Even a constant luminosity at the base can produce very complex time histories at the stellar surface. A simple pressure balance explains some features of the jet/cocoon/star interaction and allows quantitative computations Jet can propagate fast in very massive stars if compact ( ~0.3 robust). PopIII GRBs? Jet propagation takes place in 4 phases: 3 radiative Cocoon = Precursor but we do not see shocked or un-shocked jet. Different observers are however dominated by different phases. Even a constant luminosity at the base can produce very complex time histories at the stellar surface.
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