scholarly journals Instability of twisted magnetar magnetospheres

2019 ◽  
Vol 490 (4) ◽  
pp. 4858-4876
Author(s):  
J F Mahlmann ◽  
T Akgün ◽  
J A Pons ◽  
M A Aloy ◽  
P Cerdá-Durán
Keyword(s):  
Magnetic Field ◽  
Energy Dissipation ◽  
High Energy ◽  
Instability Criterion ◽  
Equilibrium Solutions ◽  
Shafranov Equation ◽  
Energy Equilibrium ◽  
Field Lines ◽  
Giant Flare ◽  
Unstable Branch

ABSTRACT We present 3D force-free electrodynamics simulations of magnetar magnetospheres that demonstrate the instability of certain degenerate, high energy equilibrium solutions of the Grad–Shafranov equation. This result indicates the existence of an unstable branch of twisted magnetospheric solutions and allows us to formulate an instability criterion. The rearrangement of magnetic field lines as a consequence of this instability triggers the dissipation of up to 30 per cent of the magnetospheric energy on a thin layer above the magnetar surface. During this process, we predict an increase of the mechanical stresses on to the stellar crust, which can potentially result in a global mechanical failure of a significant fraction of it. We find that the estimated energy release and the emission properties are compatible with the observed giant flare events. The newly identified instability is a candidate for recurrent energy dissipation, which could explain part of the phenomenology observed in magnetars.

scholarly journals Very High-Energy Emission from the Direct Vicinity of Rapidly Rotating Black Holes

Galaxies ◽  
2018 ◽  
Vol 6 (4) ◽  
pp. 122 ◽  
Author(s):  
Kouichi Hirotani
Keyword(s):  
Magnetic Field ◽  
Black Holes ◽  
Black Hole ◽  
Electric Field ◽  
Gamma Rays ◽  
Accretion Rate ◽  
High Energy ◽  
Relativistic Electrons ◽  
Field Lines ◽  
The Magnetic Field

When a black hole accretes plasmas at very low accretion rate, an advection-dominated accretion flow (ADAF) is formed. In an ADAF, relativistic electrons emit soft gamma-rays via Bremsstrahlung. Some MeV photons collide with each other to materialize as electron-positron pairs in the magnetosphere. Such pairs efficiently screen the electric field along the magnetic field lines, when the accretion rate is typically greater than 0.03–0.3% of the Eddington rate. However, when the accretion rate becomes smaller than this value, the number density of the created pairs becomes less than the rotationally induced Goldreich–Julian density. In such a charge-starved magnetosphere, an electric field arises along the magnetic field lines to accelerate charged leptons into ultra-relativistic energies, leading to an efficient TeV emission via an inverse-Compton (IC) process, spending a portion of the extracted hole’s rotational energy. In this review, we summarize the stationary lepton accelerator models in black hole magnetospheres. We apply the model to super-massive black holes and demonstrate that nearby low-luminosity active galactic nuclei are capable of emitting detectable gamma-rays between 0.1 and 30 TeV with the Cherenkov Telescope Array.

scholarly journals Magnetized Black Holes: Ionized Keplerian Disks and Acceleration of Ultra-High Energy Particles

Proceedings ◽  
2019 ◽  
Vol 17 (1) ◽  
pp. 13 ◽  
Author(s):  
Zdeněk Stuchlík ◽  
Martin Kološ ◽  
Arman Tursunov
Keyword(s):  
Magnetic Field ◽  
Black Holes ◽  
Magnetic Fields ◽  
High Energy ◽  
Weak Magnetic Fields ◽  
Motion Transformation ◽  
Penrose Process ◽  
Field Lines ◽  
High Energy Particles ◽  
Quasiperiodic Oscillations

Properties of charged particle motion in the field of magnetized black holes (BHs) imply four possible regimes of behavior of ionized Keplerian disks: survival in regular epicyclic motion, transformation into chaotic toroidal state, destruction due to fall into the BHs, destruction due to escape along magnetic field lines (escape to infinity for disks orbiting Kerr BHs). The regime of the epicyclic motion influenced by very weak magnetic fields can be related to the observed high-frequency quasiperiodic oscillations. In the case of very strong magnetic fields particles escaping to infinity could form UHECR due to extremely efficient magnetic Penrose process – protons with energy E > 10 21 eV can be accelerated by supermassive black holes with M ∼ 10 10 M ⊙ immersed in magnetic field with B ∼ 10 4 Gs.

Kinetics of Fast Component and Energy Balance of the Plasma in Gas Dynamic System With Solenoidal Magnetic Field

2010 ◽  
Author(s):  
Alexei Chirkov ◽  
Sergey Kaskov
Keyword(s):  
Magnetic Field ◽  
Collision Operator ◽  
High Energy ◽  
Plasma Parameters ◽  
Magnetic Mirrors ◽  
Gas Dynamic ◽  
Barrier Formation ◽  
Maxwellian Plasma ◽  
Field Lines ◽  
Fast Ion

Numerical model of ion kinetics is considered for the axially symmetrical magnetic trap. Magnetic system of the trap consists of long solenoid and two end coils which constrict magnetic field lines and form so-called magnetic mirrors reflecting charged particles. The trap contains warm Maxwellian plasma and strongly non-Maxwellian high-energy (fast) ions. Steady-state fast ion population supported by the ionization of high-energy neutral atoms injected into the plasma. Physical model is based on the kinetic equation with two-dimensional Fokker–Planck collision operator in the velocity phase space. Regimes of plasma exhaust trough the mirrors are considered taking into account possibility of electrostatic barrier formation. Such regimes essentially differ from gas dynamic exhaust of the warm Maxwellian plasma. Parameters of power balance for the system under consideration are discussed.

Magnetic Fields in Slowly Rotating Stars

1968 ◽  
Vol 1 (3) ◽  
pp. 89-89
Author(s):  
G.F. Davies
Keyword(s):  
Magnetic Field ◽  
Thermal Equilibrium ◽  
Meridional Circulation ◽  
Rotating Stars ◽  
Axially Symmetric ◽  
Equilibrium Solutions ◽  
Azimuthal Component ◽  
Special Cases ◽  
Field Lines ◽  
Rotating Star

Those solutions which have so far been obtained to the problem of a star with both rotation and a magnetic field have been for certain special cases, mostly time-independent. It is known that, except for stars with special rotation laws, a rotating star in hydrostatic equilibrium cannot maintain thermal equilibrium without generating slow meridional circulation of matter. It is also known that an axially symmetric field with no azimuthal component tends very strongly to keep the star in a state of isorotation, with the angular velocity constant along field lines. A magnetic field also tends to upset thermal equilibrium and produce meridional circulation. In the absence of rotation, an equilibrium poloidal field has recently been found for which there is no circulation. The present paper reports analogous equilibrium solutions for a star which is in uniform rotation.

scholarly journals Magnetized Neutron Stars

2017 ◽  
Vol 45 ◽  
pp. 1760032
Author(s):  
Gibran H. de Souza ◽  
Ernesto Kemp ◽  
Cecilia Chirenti
Keyword(s):  
Magnetic Field ◽  
Neutron Star ◽  
Neutron Stars ◽  
Numerical Solutions ◽  
Internal Magnetic Field ◽  
Shafranov Equation ◽  
Field Lines

In this work we show the results for numerical solutions of the relativistic Grad-Shafranov equation for a typical neutron star with 1.4 solar masses. We have studied the internal magnetic field considering both the poloidal and toroidal components, as well as the behavior of the field lines parametrized by the ratio between these components of the field.

scholarly journals Electron dynamics during substorm dipolarization in Mercury's magnetosphere

2005 ◽  
Vol 23 (10) ◽  
pp. 3389-3398 ◽  
Author(s):  
D. C. Delcourt ◽  
K. Seki ◽  
N. Terada ◽  
Y. Miyoshi
Keyword(s):  
Magnetic Field ◽  
High Energy ◽  
Expansion Phase ◽  
Earth’S Magnetosphere ◽  
High Energy Electrons ◽  
Earth's Magnetosphere ◽  
Magnetic Field Model ◽  
Particle Simulations ◽  
Field Lines ◽  
The Magnetic Field

Abstract. We examine the nonlinear dynamics of electrons during the expansion phase of substorms at Mercury using test particle simulations. A simple model of magnetic field line dipolarization is designed by rescaling a magnetic field model of the Earth's magnetosphere. The results of the simulations demonstrate that electrons may be subjected to significant energization on the time scale (several seconds) of the magnetic field reconfiguration. In a similar manner to ions in the near-Earth's magnetosphere, it is shown that low-energy (up to several tens of eV) electrons may not conserve the second adiabatic invariant during dipolarization, which leads to clusters of bouncing particles in the innermost magnetotail. On the other hand, it is found that, because of the stretching of the magnetic field lines, high-energy electrons (several keVs and above) do not behave adiabatically and possibly experience meandering (Speiser-type) motion around the midplane. We show that dipolarization of the magnetic field lines may be responsible for significant, though transient, (a few seconds) precipitation of energetic (several keVs) electrons onto the planet's surface. Prominent injections of energetic trapped electrons toward the planet are also obtained as a result of dipolarization. These injections, however, do not exhibit short-lived temporal modulations, as observed by Mariner-10, which thus appear to follow from a different mechanism than a simple convection surge.

scholarly journals Generalized Ohm's Laws for Relativistically Streaming Plasmas

1977 ◽  
Vol 30 (4) ◽  
pp. 471 ◽  
Author(s):  
RR Burman
Keyword(s):  
Magnetic Field ◽  
Energy Dissipation ◽  
Theoretical Framework ◽  
Inertial Effects ◽  
Field Lines

A theoretical framework is given for treating energy dissipation and the associated diffusion of magnetic field lines resulting from 'frictional' interactions between different species in plasmas in which the species have relativistic streaming velocities. The plasmas are not necessarily neutral. One result is a form for generalized Ohm's laws. Details are given for binary plasmas, with particular attention paid to the analysis of inertial effects. Some remarks are made on the relevance of the results to pulsar magnetospheres.

Magnetic Field Structures for Inverse Polarity Prominences

1994 ◽  
Vol 144 ◽  
pp. 335-338
Author(s):  
A. O. Schönfelder ◽  
A. W. Hood ◽  
R. A. S. Fiedler
Keyword(s):  
Magnetic Field ◽  
Equilibrium Equation ◽  
Numerical Solutions ◽  
Neutral Point ◽  
Coronal Plasma ◽  
Photospheric Field ◽  
Shafranov Equation ◽  
Field Lines ◽  
The Magnetic Field ◽  
Correct Topology

AbstractObservations (Leroy, 1985) have shown that most large, high prominences are of the inverse polarity type, in that the magnetic field passes through the prominence in the inverse direction to that expected from the observed photospheric field. The classic inverse polarity model of Kuperus and Raadu (1974) assumed that the prominence lies below a region of closed magnetic field lines in the neighbourhood of an O-type neutral point and above an X-type neutral point. Since the prominence must form in a low-βcoronal plasma, the pre-prominence magnetic field must have the correct topology for an inverse polarity configuration. In this paper a wide variety of different current profiles are considered in the Grad-Shafranov equation that is used to describe the equilibrium. The results of numerical solutions to the equilibrium equation indicate that a fully developed prominence will possess an O-type, but not in general an X-type neutral point.

scholarly journals THE GIANT FLARE FROM SGR 1806–20 AND ITS RADIO AFTERGLOW

2006 ◽  
Vol 21 (29) ◽  
pp. 2171-2188 ◽  
Author(s):  
G. B. TAYLOR ◽  
J. GRANOT
Keyword(s):  
Magnetic Field ◽  
Neutron Star ◽  
Cosmic Rays ◽  
Total Energy ◽  
High Energy ◽  
Multi Wavelength ◽  
Γ Ray ◽  
High Energy Neutrinos ◽  
Giant Flare ◽  
The Magnetic Field

The multi-wavelength observations of the 2004 December 27 Giant Flare (GF) from SGR 1806–20 and its long-lived radio afterglow are briefly reviewed. The GF appears to have been produced by a dramatic reconfiguration of the magnetic field near the surface of the neutron star, possibly accompanied by fractures in the crust. The explosive release of over 1046 erg (isotropic equivalent) powered a one-sided mildly relativistic outflow. The outflow produced a new expanding radio nebula that is still visible over a year after the GF. Also considered are the constraints on the total energy in the GF, the energy and mass in the outflow, and on the external density, as well as possible implications for short γ-ray bursts and potential signatures in high energy neutrinos, photons, or cosmic rays. Some possible future observations of this and other GFs are briefly discussed.

scholarly journals Escape of high-energy oxygen ions through magnetopause reconnection under northward IMF

2008 ◽  
Vol 26 (12) ◽  
pp. 3955-3966 ◽  
Author(s):  
S. Kasahara ◽  
H. Hasegawa ◽  
K. Keika ◽  
Y. Miyashita ◽  
M. N. Nishino ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Magnetic Reconnection ◽  
Recovery Phase ◽  
High Energy ◽  
Larmor Radius ◽  
Closed Field ◽  
Escape Route ◽  
Finite Larmor Radius ◽  
Oxygen Ions ◽  
Field Lines

Abstract. During a storm recovery phase on 15 May 2005, the Geotail spacecraft repeatedly observed high-energy (>180 keV) oxygen ions in the dayside magnetosheath near the equatorial plane. We focused on the time period from 11:20 UT to 13:00 UT, when Geotail observed the oxygen ions and the interplanetary magnetic field (IMF) was constantly northward. The magnetic reconnection occurrence northward and duskward of Geotail is indicated by the Walén analysis and convective flows in the magnetopause boundary layer. Anisotropic pitch angle distributions of ions suggest that high-energy oxygen ions escaped from the northward of Geotail along the reconnected magnetic field lines. From the low-energy particle precipitation in the polar cap observed by DMSP, which is consistent with magnetic reconnection occurring between the magnetosheath field lines and the magnetospheric closed field lines, we conclude that these oxygen ions are of ring current origin. Our results thus suggest a new escape route of oxygen ions during northward IMF. In the present event, this escape mechanism is more dominant than the leakage via the finite Larmor radius effect across the dayside equatorial magnetopause.

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