Special Relativistic Magnetohydrodynamic Simulation of Two-Component Outflow Powered by Magnetic Explosion on Compact Stars

Abstract

The nonlinear dynamics of outflows driven by magnetic explosion on the surface of a compact star is investigated through special relativistic magnetohydrodynamic simulations. We adopt, as the initial equilibrium state, a spherical stellar object embedded in hydrostatic plasma which has a density $\rho (r)\propto r^{-\alpha }$ and is threaded by a dipole magnetic field. The injection of magnetic energy at the surface of compact star breaks the equilibrium and triggers a two-component outflow. At the early evolutionary stage, the magnetic pressure increases rapidly around the stellar surface, initiating a magnetically driven outflow. A strong forward shock driven outflow is then excited. The expansion velocity of the magnetically driven outflow is characterized by the Alfvén velocity on the stellar surface, and follows a simple scaling relation $v_{\mathrm{mag}}\propto {v_{\mathrm{A}}}^{1/2}$. When the initial density profile declines steeply with radius, the strong shock is accelerated self-similarly to relativistic velocity ahead of the magnetically driven component. We find that it evolves according to a self-similar relation ${\Gamma }_{\mathrm{sh}}\propto r_{\mathrm{sh}}$, where ${\Gamma }_{\mathrm{sh}}$ is the Lorentz factor of the plasma measured at the shock surface $r_{\mathrm{sh}}$. Purely hydrodynamic process would be responsible for the acceleration mechanism of the shock driven outflow. Our two-component outflow model, which is the natural outcome of the magnetic explosion, can provide a better understanding of the magnetic active phenomena on various magnetized compact stars.

Accepted for publication in ApJ. 15 pages, 2 tables, 17 figures

References in corpus (4)

• Physics of Strongly Magnetized Neutron Stars
• The strongest cosmic magnets: Soft Gamma-ray Repeaters and Anomalous X-ray Pulsars
• Formation of protostellar jets as two-component outflows from star-disk magnetospheres
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• Symmetrizations of RMHD equations and stability of relativistic current-vortex sheets