Magnetic Topology in Coupled Binaries, Spin-orbital Resonances, and Flares

Abstract We consider topological configurations of the magnetically coupled spinning stellar binaries (e.g., merging neutron stars or interacting star–planet systems). We discuss conditions when the stellar spins and the orbital motion nearly “compensate” each other, leading to very slow overall winding of the coupled magnetic fields; slowly winding configurations allow gradual accumulation of magnetic energy, which is eventually released in a flare when the instability threshold is reached. We find that this slow winding can be global and/or local. We describe the topology of the relevant space F = T 1 S 2 as the unit tangent bundle of the two-sphere and find conditions for slowly winding configurations in terms of magnetic moments, spins, and orbital momentum. These conditions become ambiguous near the topological bifurcation points; in certain cases, they also depend on the relative phases of the spin and orbital motions. In the case of merging magnetized neutron stars, if one of the stars is a millisecond pulsar, spinning at ∼10 ms, the global resonance ω 1 + ω 2 = 2Ω (spin-plus beat is two times the orbital period) occurs approximately one second before the merger; the total energy of the flare can be as large as 10% of the total magnetic energy, producing bursts of luminosity ∼1044 erg s−1. Higher order local resonances may have similar powers, since the amount of involved magnetic flux tubes may be comparable to the total connected flux.

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The Influence of Binarity on Stellar Activity

Proceedings of the International Astronomical Union ◽

10.1017/s1743921307004425 ◽

2006 ◽

Vol 2 (S240) ◽

pp. 442-452 ◽

Cited By ~ 1

Author(s):

Katalin Oláh

Keyword(s):

Binary Systems ◽

Magnetic Energy ◽

Theoretical Calculations ◽

Deep Convection ◽

Magnetic Activity ◽

Close Binary ◽

Convective Envelope ◽

Flux Tubes ◽

Gravitational Forces ◽

Magnetic Flux Tubes

AbstractActivity of late type stars is enhanced by fast rotation, which is maintained in nearly synchronized close binary systems. Magnetic activity originates in the deep convection zones of stars from where magnetic flux tubes emerge to their surfaces. The gravitational forces in binaries help the clustering of activity features giving rise to active longitudes. These preferred longitudes are observed in binaries from dwarfs to giants. Differential rotation is found in many active stars that are components of binary systems. If these binaries are circularized and nearly synchronized, then there will be a corotation latitude in their surfaces, and its position can be determined by observations and by theoretical calculations. Enhanced activity in binaries could have a reverse effect as well: strong magnetism in a binary component can modify the orbital period by the cyclic exchange of kinetic and magnetic energy in its convective envelope.

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Multi-scale dynamics of magnetic flux tubes and inverse magnetic energy transfer

Journal of Plasma Physics ◽

10.1017/s0022377820000641 ◽

2020 ◽

Vol 86 (4) ◽

Author(s):

Muni Zhou ◽

Nuno F. Loureiro ◽

Dmitri A. Uzdensky

Keyword(s):

Magnetic Flux ◽

Time Evolution ◽

Magnetic Energy ◽

Numerical Study ◽

Three Dimensional ◽

Early Time ◽

Small Scale ◽

Flux Tubes ◽

Seed Field ◽

Magnetic Flux Tubes

We report on an analytical and numerical study of the dynamics of a three-dimensional array of identical magnetic flux tubes in the reduced-magnetohydrodynamic description of the plasma. We propose that the long-time evolution of this system is dictated by flux-tube mergers, and that such mergers are dynamically constrained by the conservation of the pertinent (ideal) invariants, viz. the magnetic potential and axial fluxes of each tube. We also propose that in the direction perpendicular to the merging plane, flux tubes evolve in a critically balanced fashion. These notions allow us to construct an analytical model for how quantities such as the magnetic energy and the energy-containing scale evolve as functions of time. Of particular importance is the conclusion that, like its two-dimensional counterpart, this system exhibits an inverse transfer of magnetic energy that terminates only at the system scale. We perform direct numerical simulations that confirm these predictions and reveal other interesting aspects of the evolution of the system. We find, for example, that the early time evolution is characterized by a sharp decay of the initial magnetic energy, which we attribute to the ubiquitous formation of current sheets. We also show that a quantitatively similar inverse transfer of magnetic energy is observed when the initial condition is a random, small-scale magnetic seed field.

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Decay of trefoil and other magnetic knots

Proceedings of the International Astronomical Union ◽

10.1017/s1743921311007496 ◽

2010 ◽

Vol 6 (S274) ◽

pp. 461-463 ◽

Cited By ~ 2

Author(s):

Simon Candelaresi ◽

Fabio Del Sordo ◽

Axel Brandenburg

Keyword(s):

Magnetic Flux ◽

Magnetic Energy ◽

Field Configuration ◽

The Other ◽

Flux Tubes ◽

Trefoil Knot ◽

Magnetic Flux Tubes ◽

Field Lines

AbstractTwo setups with interlocked magnetic flux tubes are used to study the evolution of magnetic energy and helicity on magnetohydrodynamical (MHD) systems like plasmas. In one setup the initial helicity is zero while in the other it is finite. To see if it is the actual linking or merely the helicity content that influences the dynamics of the system we also consider a setup with unlinked field lines as well as a field configuration in the shape of a trefoil knot. For helical systems the decay of magnetic energy is slowed down by the helicity which decays slowly. It turns out that it is the helicity content, rather than the actual linking, that is significant for the dynamics.

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Particle acceleration in relativistic magnetic flux-merging events

Journal of Plasma Physics ◽

10.1017/s002237781700071x ◽

2017 ◽

Vol 83 (6) ◽

Cited By ~ 18

Author(s):

Maxim Lyutikov ◽

Lorenzo Sironi ◽

Serguei S. Komissarov ◽

Oliver Porth

Keyword(s):

Magnetic Field ◽

Particle Acceleration ◽

Magnetic Flux ◽

Power Law ◽

Magnetic Energy ◽

Thermal Power ◽

Local Magnetic Field ◽

Flux Tubes ◽

Maximal Energy ◽

Magnetic Flux Tubes

Using analytical and numerical methods (fluid and particle-in-cell simulations) we study a number of model problems involving merger of magnetic flux tubes in relativistic magnetically dominated plasma. Mergers of current-carrying flux tubes (exemplified by the two-dimensional ‘ABC’ structures) and zero-total-current magnetic flux tubes are considered. In all cases regimes of spontaneous and driven evolution are investigated. We identify two stages of particle acceleration during flux mergers: (i) fast explosive prompt X-point collapse and (ii) ensuing island merger. The fastest acceleration occurs during the initial catastrophic X-point collapse, with the reconnection electric field of the order of the magnetic field. During the X-point collapse, particles are accelerated by charge-starved electric fields, which can reach (and even exceed) values of the local magnetic field. The explosive stage of reconnection produces non-thermal power-law tails with slopes that depend on the average magnetization $\unicode[STIX]{x1D70E}$. For plasma magnetization $\unicode[STIX]{x1D70E}\leqslant 10^{2}$ the spectrum power-law index is $p>2$; in this case the maximal energy depends linearly on the size of the reconnecting islands. For higher magnetization, $\unicode[STIX]{x1D70E}\geqslant 10^{2}$, the spectra are hard, $p<2$, yet the maximal energy $\unicode[STIX]{x1D6FE}_{\text{max}}$ can still exceed the average magnetic energy per particle, ${\sim}\unicode[STIX]{x1D70E}$, by orders of magnitude (if $p$ is not too close to unity). The X-point collapse stage is followed by magnetic island merger that dissipates a large fraction of the initial magnetic energy in a regime of forced magnetic reconnection, further accelerating the particles, but proceeds at a slower reconnection rate.

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Color-magnetic flux tubes in quark matter cores of neutron stars

Journal of Physics G Nuclear and Particle Physics ◽

10.1088/0954-3899/37/7/075202 ◽

2010 ◽

Vol 37 (7) ◽

pp. 075202 ◽

Cited By ~ 25

Author(s):

Mark G Alford ◽

Armen Sedrakian

Keyword(s):

Magnetic Flux ◽

Neutron Stars ◽

Quark Matter ◽

Flux Tubes ◽

Magnetic Flux Tubes

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Linear Visco-Resistive Computations of Magnetohydrodynamic Waves: I. The Code and Test Cases

International Astronomical Union Colloquium ◽

10.1017/s0252921100025926 ◽

1994 ◽

Vol 144 ◽

pp. 503-505

Author(s):

R. Erdélyi ◽

M. Goossens ◽

S. Poedts

Keyword(s):

Resonant Absorption ◽

Numerical Code ◽

Mhd Waves ◽

Test Cases ◽

Numerical Accuracy ◽

Element Discretization ◽

Flux Tubes ◽

Magnetohydrodynamic Waves ◽

Viscosity Coefficients ◽

Magnetic Flux Tubes

AbstractThe stationary state of resonant absorption of linear, MHD waves in cylindrical magnetic flux tubes is studied in viscous, compressible MHD with a numerical code using finite element discretization. The full viscosity tensor with the five viscosity coefficients as given by Braginskii is included in the analysis. Our computations reproduce the absorption rates obtained by Lou in scalar viscous MHD and Goossens and Poedts in resistive MHD, which guarantee the numerical accuracy of the tensorial viscous MHD code.

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Search for intermittent X-ray pulsations from neutron stars in low-mass X-ray binaries

Publications of the Astronomical Society of Australia ◽

10.1017/pasa.2021.6 ◽

2021 ◽

Vol 38 ◽

Author(s):

Yunus Emre Bahar ◽

Manoneeta Chakraborty ◽

Ersin Göğüş

Keyword(s):

Neutron Stars ◽

Orbital Period ◽

Oscillation Frequency ◽

Orbital Motion ◽

X Rays ◽

X Ray ◽

Second Stage ◽

Corrected Data ◽

Low Mass ◽

X Ray Binaries

Abstract We present the results of our extensive binary orbital motion corrected pulsation search for 13 low-mass X-ray binaries. These selected sources exhibit burst oscillations in X-rays with frequencies ranging from 45 to 1 122 Hz and have a binary orbital period varying from 2.1 to 18.9 h. We first determined episodes that contain weak pulsations around the burst oscillation frequency by searching all archival Rossi X-ray Timing Explorer data of these sources. Then, we applied Doppler corrections to these pulsation episodes to discard the smearing effect of the binary orbital motion and searched for recovered pulsations at the second stage. Here we report 75 pulsation episodes that contain weak but coherent pulsations around the burst oscillation frequency. Furthermore, we report eight new episodes that show relatively strong pulsations in the binary orbital motion corrected data.

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Resonant Instability of Kink Oscillations in Magnetic Flux Tubes with Siphon Flow

Solar Physics ◽

10.1007/s11207-021-01842-0 ◽

2021 ◽

Vol 296 (6) ◽

Author(s):

Michael S. Ruderman ◽

Nikolai S. Petrukhin

Keyword(s):

Flow Velocity ◽

Resonant Absorption ◽

Tube Axis ◽

Magnetic Tube ◽

Transitional Layer ◽

Threshold Velocity ◽

Flux Tubes ◽

Resonant Instability ◽

Constant Magnitude ◽

Magnetic Flux Tubes

AbstractWe study kink oscillations of a straight magnetic tube in the presence of siphon flows. The tube consists of a core and a transitional or boundary layer. The flow velocity is parallel to the tube axis, has constant magnitude, and confined in the tube core. The plasma density is constant in the tube core and it monotonically decreases in the transitional layer to its value in the surrounding plasma. We use the expression for the decrement/increment previously obtained by Ruderman and Petrukhin (Astron. Astrophys.631, A31, 2019) to study the damping and resonant instability of kink oscillations. We show that, depending on the magnitude of siphon-velocity, resonant absorption can cause either the damping of kink oscillations or their enhancement. There are two threshold velocities: When the flow velocity is below the first threshold velocity, kink oscillations damp. When the flow velocity is above the second threshold velocity, the kink oscillation amplitudes grow. Finally, when the flow velocity is between the two threshold velocities, the oscillation amplitudes do not change. We apply the theoretical result to kink oscillations of prominence threads. We show that, for particular values of thread parameters, resonant instability can excite these kink oscillations.

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