The Termination Shock in a Striped Pulsar Wind

Toroidal stripes of opposite magnetic polarity are formed in the equatorial belt of the wind emanating from an obliquely rotating pulsar magnetosphere. Such a striped wind transfers most of its spindown energy because the angular distribution of the energy flux in the pulsar wind is maximum at the equator. The alternating field annihilates either in the pulsar wind or at the termination shock so that the flow in the equatorial belt downstream of the termination shock is weakly magnetized. At high latitudes, the magnetization of the flow is higher than in the equatorial belt whereas the total energy flux is smaller. At such a distribution of the energy flux and magnetization, the downstream flow separates into an equatorial disk and a magnetically collimated polar jet. Particle acceleration at the termination shock in a striped wind is discussed. It is argued that the radio emitting electrons are accelerated by driven reconnection of the alternating field at the shock whereas the Fermi acceleration of electrons preaccelerated in the reconnection process results in a high energy tail responsible for the X- and γ-ray emission.

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High-energy flux evolution of Pulsar Wind Nebulae

10.1063/1.3076667 ◽

2008 ◽

Author(s):

F. Mattana ◽

M. Falanga ◽

D. Götz ◽

R. Terrier ◽

P. Esposito ◽

...

Keyword(s):

Energy Flux ◽

High Energy ◽

Pulsar Wind Nebulae ◽

Pulsar Wind

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RELAXATION OF PULSAR WIND NEBULA VIA CURRENT-DRIVEN KINK INSTABILITY

International Journal of Modern Physics Conference Series ◽

10.1142/s2010194512004916 ◽

2012 ◽

Vol 08 ◽

pp. 368-371

Author(s):

YOSUKE MIZUNO ◽

YURI LYUBARSKY ◽

KEN-ICHI NISHIKAWA ◽

PHILIP E. HARDEE

Keyword(s):

Energy Flux ◽

Plasma Column ◽

Hoop Stress ◽

Magnetic Energy ◽

Pulsar Wind Nebulae ◽

Initial Value ◽

Hot Plasma ◽

Total Energy Flux ◽

Pulsar Wind ◽

Kink Instability

We have investigated the relaxation of a hydrostatic hot plasma column containing toroidal magnetic field by the Current-Driven (CD) kink instability as a model of pulsar wind nebulae. In our simulations the CD kink instability was excited by a small initial velocity perturbation and developed turbulent structure inside the hot plasma column. We demonstrated that, as envisioned by Begelman, the hoop stress declines and the initial gas pressure excess near the axis decreases. The magnetization parameter "σ", the ratio of the magnetic energy to the thermal energy for a hot plasma, declined from an initial value of 0.3 to about 0.01 when the CD kink instability saturated. Our simulations demonstrated that axisymmetric models strongly overestimate the elongation of the pulsar wind nebulae. Therefore, the previous requirement for an extremely low pulsar wind magnetization can be abandoned. The observed structure of the pulsar wind nebulae do not contradict the natural assumption that the magnetic energy flux still remains a good fraction of the total energy flux after dissipation of alternating fields.

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ON COSMIC RAY ACCELERATION IN RELATIVISTIC JETS

International Journal of Modern Physics D ◽

10.1142/s0218271808013467 ◽

2008 ◽

Vol 17 (10) ◽

pp. 1827-1837

Author(s):

MICHAL OSTROWSKI

Keyword(s):

Cosmic Ray ◽

Lorentz Factor ◽

High Energy ◽

Fermi Acceleration ◽

High Energy Part ◽

Particle Distributions ◽

Cygnus A ◽

Relativistic Shocks ◽

Energy Part ◽

High Energy Tail

We review the theoretical progress in the field of cosmic-ray first-order Fermi acceleration at relativistic shock fronts, showing that recent results change our knowledge about these processes substantially. In particular, relativistic shocks are unlikely to form particle distributions extending to very high energies. Instead, recent simulations give particle distributions where a shock-compressed injected component is followed by a more or less extended high energy tail. An increase of the Lorentz factor of the shock usually leads to steepening and a decrease of the energetic tail, so that fitted spectral indices to the high energy part can substantially deviate from the "universal power law index" σ ≈ 2.2. We report on observational findings from the hot spots in Cygnus A, showing that the derived electron spectra (with a very flat, σ ≈ 1.5, low energy part up to ~ 1 GeV, followed by a much steeper, σ > 3, part at higher energies) indeed deviate from the standard expectation for relativistic shocks. We conclude with a short discussion of some qualitative features of shear and second-order Fermi acceleration in turbulent relativistic plasmas.

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H.E.S.S. and Suzaku observations of the Vela X pulsar wind nebula

Astronomy and Astrophysics ◽

10.1051/0004-6361/201935458 ◽

2019 ◽

Vol 627 ◽

pp. A100 ◽

Cited By ~ 2

Author(s):

◽

H. Abdalla ◽

F. Aharonian ◽

F. Ait Benkhali ◽

E. O. Angüner ◽

...

Keyword(s):

Magnetic Field ◽

Magnetic Fields ◽

Gamma Ray ◽

High Energy ◽

Termination Shock ◽

Reverse Shock ◽

X Ray ◽

Electron Spectra ◽

Very High Energy ◽

Pulsar Wind

Context. Pulsar wind nebulae (PWNe) represent the most prominent population of Galactic very-high-energy gamma-ray sources and are thought to be an efficient source of leptonic cosmic rays. Vela X is a nearby middle-aged PWN, which shows bright X-ray and TeV gamma-ray emission towards an elongated structure called the cocoon. Aims. Since TeV emission is likely inverse-Compton emission of electrons, predominantly from interactions with the cosmic microwave background, while X-ray emission is synchrotron radiation of the same electrons, we aim to derive the properties of the relativistic particles and of magnetic fields with minimal modelling. Methods. We used data from the Suzaku XIS to derive the spectra from three compact regions in Vela X covering distances from 0.3 to 4 pc from the pulsar along the cocoon. We obtained gamma-ray spectra of the same regions from H.E.S.S. observations and fitted a radiative model to the multi-wavelength spectra. Results. The TeV electron spectra and magnetic field strengths are consistent within the uncertainties for the three regions, with energy densities of the order 10−12 erg cm−3. The data indicate the presence of a cutoff in the electron spectrum at energies of ~ 100 TeV and a magnetic field strength of ~6 μG. Constraints on the presence of turbulent magnetic fields are weak. Conclusions. The pressure of TeV electrons and magnetic fields in the cocoon is dynamically negligible, requiring the presence of another dominant pressure component to balance the pulsar wind at the termination shock. Sub-TeV electrons cannot completely account for the missing pressure, which may be provided either by relativistic ions or from mixing of the ejecta with the pulsar wind. The electron spectra are consistent with expectations from transport scenarios dominated either by advection via the reverse shock or by diffusion, but for the latter the role of radiative losses near the termination shock needs to be further investigated in the light of the measured cutoff energies. Constraints on turbulent magnetic fields and the shape of the electron cutoff can be improved by spectral measurements in the energy range ≳ 10 keV.

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Effects of the solar wind termination shock and heliosheath on theheliospheric modulation of galactic and anomalous Helium

Annales Geophysicae ◽

10.5194/angeo-22-3063-2004 ◽

2004 ◽

Vol 22 (8) ◽

pp. 3063-3072 ◽

Cited By ~ 15

Author(s):

U. W. Langner ◽

M. S. Potgieter

Keyword(s):

Solar Wind ◽

Cosmic Ray ◽

Magnetic Polarity ◽

Termination Shock ◽

Shock Acceleration ◽

Diffusive Shock Acceleration ◽

Cosmic Ray Modulation ◽

Low Energies ◽

Solar Wind Termination Shock ◽

Charge Sign

Abstract. The interest in the role of the solar wind termination shock and heliosheath in cosmic ray modulation studies has increased significantly as the Voyager 1 and 2 spacecraft approach the estimated position of the solar wind termination shock. The effect of the solar wind termination shock on charge-sign dependent modulation, as is experienced by galactic cosmic ray Helium (He++) and anomalous Helium (He+), is the main topic of this work, and is complementary to the previous work on protons, anti-protons, electrons, and positrons. The modulation of galactic and anomalous Helium is studied with a numerical model including a more fundamental and comprehensive set of diffusion coefficients, a solar wind termination shock with diffusive shock acceleration, a heliosheath and particle drifts. The model allows a comparison of modulation with and without a solar wind termination shock and is applicable to a number of cosmic ray species during both magnetic polarity cycles of the Sun. The modulation of Helium, including an anomalous component, is also done to establish charge-sign dependence at low energies. We found that the heliosheath is important for cosmic ray modulation and that its effect on modulation is very similar for protons and Helium. The local Helium interstellar spectrum may not be known at energies

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Electromagnetic power of lightning superbolts from Earth to space

Nature Communications ◽

10.1038/s41467-021-23740-6 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

J.-F. Ripoll ◽

T. Farges ◽

D. M. Malaspina ◽

G. S. Cunningham ◽

E. H. Lay ◽

...

Keyword(s):

Low Frequency ◽

Optical Emission ◽

High Energy ◽

Very Low Frequency ◽

Electromagnetic Power ◽

Power Spectral ◽

High Energy Tail ◽

Van Allen Probes ◽

Long Time ◽

Low Frequency Waves

AbstractLightning superbolts are the most powerful and rare lightning events with intense optical emission, first identified from space. Superbolt events occurred in 2010-2018 could be localized by extracting the high energy tail of the lightning stroke signals measured by the very low frequency ground stations of the World-Wide Lightning Location Network. Here, we report electromagnetic observations of superbolts from space using Van Allen Probes satellite measurements, and ground measurements, and with two events measured both from ground and space. From burst-triggered measurements, we compute electric and magnetic power spectral density for very low frequency waves driven by superbolts, both on Earth and transmitted into space, demonstrating that superbolts transmit 10-1000 times more powerful very low frequency waves into space than typical strokes and revealing that their extreme nature is observed in space. We find several properties of superbolts that notably differ from most lightning flashes; a more symmetric first ground-wave peak due to a longer rise time, larger peak current, weaker decay of electromagnetic power density in space with distance, and a power mostly confined in the very low frequency range. Their signal is absent in space during day times and is received with a long-time delay on the Van Allen Probes. These results have implications for our understanding of lightning and superbolts, for ionosphere-magnetosphere wave transmission, wave propagation in space, and remote sensing of extreme events.

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Introducing the HD+B model for pulsar wind nebulae: a hybrid hydrodynamics/radiative approach

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1052 ◽

2020 ◽

Vol 494 (3) ◽

pp. 4357-4370

Author(s):

B Olmi ◽

D F Torres

Keyword(s):

Gamma Ray ◽

High Energy ◽

Theoretical Modelling ◽

X Rays ◽

Pulsar Wind Nebulae ◽

New Approach ◽

Energy Gamma ◽

Radiative Model ◽

Pulsar Wind

ABSTRACT Identification and characterization of a rapidly increasing number of pulsar wind nebulae is, and will continue to be, a challenge of high-energy gamma-ray astrophysics. Given that such systems constitute -by far- the most numerous expected population in the TeV regime, such characterization is important not only to learn about the sources per se from an individual and population perspective, but also to be able to connect them with observations at other frequencies, especially in radio and X-rays. Also, we need to remove the emission from nebulae in highly confused regions of the sky for revealing other underlying emitters. In this paper, we present a new approach for theoretical modelling of pulsar wind nebulae: a hybrid hydrodynamic-radiative model able to reproduce morphological features and spectra of the sources, with relatively limited numerical cost.

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