147 research outputs found
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
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