2008/04/30 by Hayato Mikami, Yuji Sato, Tomoaki Matsumoto +1 · 2 citations
Physics and Astronomy · #Gamma-ray bursts and supernovae #Instability #Magnetic energy #Magnetic field #Magnetic pressure #Magnetohydrodynamics #Neutrino Physics Research #Pulsars and Gravitational Waves Research #Rotation (mathematics) #Stars #Supernova #astro-ph
paper · pdf · doi:10.1086/589759
41 pages, 24 figures, 4 tables, accepted for publication in ApJ. The high resolution version is available at http://www.astro.phys.s.chiba-u.ac.jp/~mikami/research/
arxiv created 2008/05/07 · openalex publication_date 2008/08/07 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We show three-dimensional magnetohydrodynamical simulations of a core-collapse supernova in which the progenitor has magnetic fields inclined to the rotation axis. The simulations employed a simple empirical equation of state in which the pressure of degenerate gas is approximated by piecewise polytropes for simplicity. Energy loss due to neutrinos is not taken into account for simplicity as well. The simulations start from the stage of dynamical collapse of an iron core. The dynamical collapse halts at t = 189 ms by the pressure of high-density gas, and a proto-neutron star (PNS) forms. The evolution of the PNS was followed for about 40 ms in typical models. When the initial rotation is mildly fast and the initial magnetic fields are mildly strong, bipolar jets are launched from the upper atmosphere ( r ∼ 60 km ) of the PNS. The jets are accelerated to ~3 × 10 4 km s −1 , which is comparable to the escape velocity at the footpoint. The jets are parallel to the initial rotation axis. Before the launch of the jets, magnetic fields are twisted by rotation of the PNS. The twisted magnetic fields form torus-shaped multilayers in which the azimuthal component changes alternately. The formation of magnetic multilayers is due to the initial condition in which the magnetic fields are inclined with respect to the rotation axis. The energy of the jet depends only weakly on the initial magnetic field assumed. When the initial magnetic fields are weaker, the time lag is longer between the PNS formation and jet ejection. It is also shown that the time lag is related to the Alfvén transit time. Although the nearly spherical prompt shock propagates outward in our simulations, it is an artifact due to our simplified equation of state and neglect of neutrino loss. The morphology of twisted magnetic field and associate jet ejection are, however, not affected by the simplification.