Long duration gamma-ray bursts: hydrodynamic instabilities in collapsar disks

We present 3D numerical simulations of the early evolution of long-duration gamma-ray bursts in the collapsar scenario. Starting from the core-collapse of a realistic progenitor model, we follow the formation and evolution of a central black hole and centrifugally balanced disk. The dense, hot accretion disk produces freely-escaping neutrinos and is hydrodynamically unstable to clumping and to forming non-axisymmetric (m=1, 2) modes. We show that these spiral structures, which form on dynamical timescales, can efficiently transfer angular momentum outward and can drive the high required accretion rates (>=0.1-1 M_sun) for producing a jet. We utilise the smoothed particle hydrodynamics code, Gadget-2, modified to implement relevant microphysics, such as cooling by neutrinos, a plausible treatment approximating the central object and relativistic effects. Finally, we discuss implications of this scenario as a source of energy to produce relativistically beamed gamma-ray jets.

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