The Evolution of High Temperature Plasma in Magnetar Magnetospheres and its Implications for Giant Flares

In this paper we propose a new mechanism describing the initial spike of giant flares in the framework of the starquake model. We investigate the evolution of a plasma on a closed magnetic flux tube in the magnetosphere of a magnetar in the case of a sudden energy release and discuss the relationship with observations of giant flares. We perform one-dimensional numerical simulations of the relativistic magnetohydrodynamics in Schwarzschild geometry. We assume energy is injected at the footpoints of the loop by a hot star surface containing random perturbations of the transverse velocity. Alfv\'en waves are generated and propagate upward, accompanying very hot plasma that is also continuously heated by nonlinearly generated compressive waves. We find that the front edges of the fireball regions collide at the top of the tube with their symmetrically launched counterparts. This collision results in an energy release which can describe the light curve of initial spikes of giant flares.Comment: 13 pages, 11 figures, accepted for publication in Ap

Solar-type Magnetic Reconnection Model for Magnetar Giant Flare

We present a theoretical model describing magnetar giant flares on the basis of solar flare/coronal mass ejection theory. In our model, a preflare activity plays a crucial role in driving evaporating flows and supplying baryonic matters into the magnetosphere. The loaded baryonic matter, that is called "prominence", is then gradually uplifted via crustal cracking with maintaining a quasi-force-free equilibrium of the magnetosphere. Finally the prominence is erupted by the magnetic pressure force due to the loss of equilibrium triggered by the explosive magnetic reconnection. The giant flare should be induced as a final outcome of the prominence eruption accompanied by large-scale field reconfigurations. An essential difference between solar and magnetar flares is the control process of their evolutionary dynamics. The flaring activity on magnetars is mainly controlled by the radiative process unlike the solar flare governed by the electron conduction. It is highly suggestive that our model is accountable for the physical properties of the extraordinary giant flare observed on 2004 December 27 from SGR1806-20, including the source of baryonic matters loaded in the expanding ejecta observed after the giant burst.Comment: Accepted for Publications of the Astronomical Society of Japan (PASJ Vol.62 No.4), 21 pages, 4 figure