17,285 research outputs found
Distribution of Faraday Rotation Measure in Jets from Active Galactic Nuclei II. Prediction from our Sweeping Magnetic Twist Model for the Wiggled Parts of AGN Jets and Tails
Distributions of Faraday rotation measure (FRM) and the projected magnetic
field derived by a 3-dimensional simulation of MHD jets are investigated based
on our "sweeping magnetic twist model". FRM and Stokes parameters were
calculated to be compared with radio observations of large scale wiggled AGN
jets on kpc scales. We propose that the FRM distribution can be used to discuss
the 3-dimensional structure of magnetic field around jets and the validity of
existing theoretical models, together with the projected magnetic field derived
from Stokes parameters. In the previous paper, we investigated the basic
straight part of AGN jets by using the result of a 2-dimensional axisymmetric
simulation. The derived FRM distribution has a general tendency to have a
gradient across the jet axis, which is due to the toroidal component of the
magnetic field generated by the rotation of the accretion disk. In this paper,
we consider the wiggled structure of the AGN jets by using the result of a
3-dimensional simulation. Our numerical results show that the distributions of
FRM and the projected magnetic field have a clear correlation with the large
scale structure of the jet itself, namely, 3-dimensional helix. Distributions,
seeing the jet from a certain direction, show a good matching with those in a
part of 3C449 jet. This suggests that the jet has a helical structure and that
the magnetic field (especially the toroidal component) plays an important role
in the dynamics of the wiggle formation because it is due to a current-driven
helical kink instability in our model.Comment: Accepted for publication in Ap
Canonical Theory of 2+1 Gravity
Recently 2+1 dimensional gravity theory, especially has been
studied extensively. It was shown to be equivalent to the 2+1 Chern-Simon
theory and has been investigated to understand the black hole thermodynamics,
i.e. Hawking temperature and others. The purpose of this report is to
investigate the canonical formalism of the original 2+1 Einstein gravity theory
instead of the Chern-Simon theory. For the spherically symmetric space-time,
local conserved quantities(local mass and angular momentum) are introduced and
using them canonical quantum theory is defined. Constraints are imposed on
state vectors and solved analytically. The strategy to obtain the solution is
followed by our previous work.Comment: 6 pages, talk given at LLWI-2000: From Particles to Universe,
Alberta, 20-26 February 200
On the Superradiance of Spin-1 Waves in an Equatorial Wedge around a Kerr Hole
Recently Van Putten has suggested that superradiance of magnetosonic waves in
a toroidal magnetosphere around a Kerr black hole may play a role in the
central engine of gamma-ray bursts. In this context, he computed (in the WKB
approximation) the superradiant amplification of scalar waves confined to a
thin equatorial wedge around a Kerr hole and found that the superradiance is
higher than for radiation incident over all angles. This paper presents
calculations of both spin-0 (scalar) superradiance (integrating the radial
equation rather than using the WKB method) and and spin-1
(electromagnetic/magnetosonic) superradiance, in Van Putten's wedge geometry.
In contrast to the scalar case, spin-1 superradiance decreases in the wedge
geometry, decreasing the likelihood of its astrophysical importance.Comment: Submitted to The Astrophysical Journal Letter
Why current-carrying magnetic flux tubes gobble up plasma and become thin as a result
It is shown that if a current-carrying magnetic flux tube is bulged at its
axial midpoint z=0 and constricted at its axial endpoints z=+h,-h, then plasma
will be accelerated from z=+h,-h towards z=0 resulting in a situation similar
to two water jets pointed at each other. The ingested plasma convects embedded,
frozen-in toroidal magnetic flux from z=+h,-h to z=0. The counter-directed
flows collide and stagnate at z=0 and in so doing (i) convert their
translational kinetic energy into heat, (ii) increase the plasma density at
z~0, and (iii) increase the embedded toroidal flux density at z~0. The increase
in toroidal flux density at z~0 increases the toroidal field Bphi and hence
increases the magnetic pinch force at z~0 and so causes a reduction of the flux
tube radius at z~0. Thus, the flux tube develops an axially uniform
cross-section, a decreased volume, an increased density, and an increased
temperature. This model is proposed as a likely hypothesis for the
long-standing mystery of why solar coronal loops are observed to be axially
uniform, hot, and bright.Comment: to appear in Physics of Plasmas 24 pages, 5 figure
Asymmetric Supernovae from Magneto-Centrifugal Jets
Strong toroidal magnetic fields generated in stellar collapse can generate
magneto-centrifugal jets in analogy to those found in simulations of black hole
accretion and explain why all core collapse supernovae are found to be
substantially asymmetric and predominantly bi-polar. We describe two phases:
the initial LeBlanc-Wilson jet and a subsequent protopulsar or toroidal jet
that propagates at about the core escape velocity. The jets will produce bow
shocks that tend to expel matter, including iron and silicon, into equatorial
tori, accounting for observations of the element distribution in Cas A. A
magnetic ``switch'' mechanism may apply in instances of low density and large
magnetic field with subsequent increase in the speed and collimation of the
toroidal jet, depositing relatively little momentum. The result could be enough
infall to form a black hole with a third, highly relativistic jet that could
catch up to the protopulsar jet after it has emerged from the star. The
interaction of these two jets could generate internal shocks and explain the
presence of iron lines in the afterglow. Recent estimates that typical
gamma-ray burst energy is about 3x10^50 erg imply either a very low efficiency
for conversion of rotation into jets, or a rather rapid turnoff of the jet
process even though the black hole still rotates rapidly. Magnetars and
``hypernovae'' might arise in an intermediate parameter regime of energetic
jets that yield larger magnetic fields and provide more energy than the routine
case, but that are not so tightly collimated that they yield failed supernova.
(slightly abridged)Comment: AASTeX, 29 pages, 2 postscript figures, accepted by ApJ, November 20,
200
Conical Singular Solutions in (2+1)-Dimensional Gravity Employing the ADM Canonical Formalism
Topological solutions in the (2+1)-dimensional Einstein theory of gravity are
studied within the ADM canonical formalism. It is found that a conical
singularity appears in the closed de Sitter universe solution as a topological
defect in the case of the Einstein theory with a cosmological constant. Quantum
effects on the conical singularity are studied using the de Broglie-Bohm
interpretation. Finite quantum tunneling effects are obtained for the closed de
Sitter universe, while no quantum effects are obtained for an open universe.Comment: 15 pages, 3 figure
Hyper- and suspended-accretion states of rotating black holes and the durations of gamma-ray bursts
We analyze the temporal evolution of accretion onto rotating black holes
subject to large-scale magnetic torques. Wind torques alone drive a disk
towards collapse in a finite time , where is the
initial free-fall time and is the ratio of kinetic-to-poloidal
magnetic energy. Additional spin-up torques from a rapidly rotating black hole
can arrest the disk's inflow. We associate short/long gamma-ray bursts with
hyperaccretion/suspended-accretion onto slowly/rapidly spinning black holes.
This model predicts afterglow emission from short bursts, and may be tested by
HETE-II.Comment: accepted for publication in the ApJ
Kaluza-Klein bubble like structure and celestial sphere in inflationary universe
We consider five dimensional deSitter spacetimes with a deficit angle due to
the presence of a closed 2-brane and identify one dimension as an extra
dimension. From the four dimensional viewpoint we can see that the spacetime
has a structure similar to a Kaluza-Klein bubble of nothing, that is, four
dimensional spacetime ends at the 2-brane. Since a spatial section of the full
deSitter spacetime has the topology of a sphere, the boundary surface surrounds
the remaining four dimensional spacetime, and can be considered as the
celestial sphere. After the spacetime is created from nothing via an instanton
which we describe, some four dimensional observers in it see the celestial
sphere falling down, and will be in contact with a 2-brane attached on it.Comment: 5pages, 4figures, to be published in GR
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