Dynamics of an Alfven surface in core collapse supernovae

Abstract

We investigate the dynamics of an Alfven surface (where the Alfven speed equals the advection velocity) in the context of core collapse supernovae during the phase of accretion on the proto-neutron star. Such a surface should exist even for weak magnetic fields because the advection velocity decreases to zero at the center of the collapsing core. In this decelerated flow, Alfven waves created by the standing accretion shock instability (SASI) or convection accumulate and amplify while approaching the Alfven surface. We study this amplification using one dimensional MHD simulations with explicit physical dissipation. In the linear regime, the amplification continues until the Alfven wavelength becomes as small as the dissipative scale. A pressure feedback that increases the pressure in the upstream flow is created via a non linear coupling. We derive analytic formulae for the maximum amplification and the non linear coupling and check them with numerical simulations to a very good accuracy. We also characterize the non linear saturation of this amplification when compression effects become important, leading to either a change of the velocity gradient, or a steepening of the Alfven wave. Applying these results to core collapse supernovae shows that the amplification can be fast enough to affect the dynamics, if the magnetic field is strong enough for the Alfven surface to lie in the region of strong velocity gradient just above the neutrinosphere. This requires the presence of a strong magnetic field in the progenitor star, which would correspond to the formation of a magnetar under the assumption of magnetic flux conservation. An extrapolation of our analytic formula (taking into account the nonlinear saturation) suggests that the Alfven wave could reach an amplitude of B ~ 10^15 G, and that the pressure feedback could significantly contribute to the pressure below the shock.

18 pages, 14 figures, accepted for publication in ApJ. Added a discussion of the energy budget in subsection 7.6

References in corpus (8)

• A High Order Godunov Scheme with Constrained Transport and Adaptive Mesh Refinement for Astrophysical MHD
• Delayed neutrino-driven supernova explosions aided by the standing accretion-shock instability
• Instability of a stalled accretion shock: evidence for the advective-acoustic cycle
• Multidimensional supernova simulations with approximative neutrino transport. II. Convection and the advective-acoustic cycle in the supernova core
• Semi-global simulations of the magneto-rotational instability in core collapse supernovae
• Magnetorotational collapse of massive stellar cores to neutron stars: Simulations in full general relativity
• Nonlinear Saturation of g-modes in Proto-Neutron Stars: Quieting the Acoustic Engine
• Alfven Wave-Driven Supernova Explosion

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