1204.4360 (K. H. Tsui et al.)

Plasma Pressure Driven Magnetic Self-Focusing of Aspherical Supernovae and Highly Collimated Gamma-Ray Bursts    [PDF]

K. H. Tsui, C. E. Navia

During the process of core-collapse of a massive star, the iron core evolves into an inner central core and an outer envelope, generating a cavity in between. The dynamics of this cavity, filled with plasma and magnetic field by the rapidly rotating pulsar (spun-down magnetar) at the center, is believed to be very relevant to account for supernovae and gamma-ray bursts \citep{uzdensky2007}. The interactions of the pressurized conducting plasma and the magnetic field could generate some spatial distributions of plasma and magnetic field within the cavity. In an effort to better understand the spatial distributions, a set of time-dependent magnetohydrodynamic (MHD) equations is used to model this cavity system. Homologous solutions in Lagrangian representation are obtained to account for the spatial structures. Under this self-similar description, the magnetic flux function is governed by an eigenvalue equation with the eigenvalue being the poloidal plasma $\beta$, which is the ratio of plasma pressure to poloidal magnetic pressure. In terms of the flux function, the magnetic fields are structured in the cavity with a set of axisymmetric lobes (magnetic vortices). Because of a geometric singularity, the magnetic lobe energy tends to collimate onto the polar axis, as a function of increasing plasma pressure in the cavity. Since this model indicates $\beta\gg 1$, plasma pressure stored in the cavity is the primary motor for supernova, not the magnetic field. At very high plasma pressure and high magnetic fields, the collimation is confined to a very small cone along the axis with a sequence of magnetic lobes, generating a configuration appropriate for gamma-ray burst with multiple fireballs.

View original: http://arxiv.org/abs/1204.4360