Interaction of pulsar winds with interstellar medium: numerical simulation

Abstract

A time‐dependent numerical simulation of relativistic wind interaction with interstellar medium was performed. The winds are ejected from the magnetosphere of rotation‐powered pulsars. The particle flux in the winds is isotropic while the energy flux is strongly anisotropic. Pure hydrodynamical winds and magnetized winds with magnetization in the range 3 × 10−3–10−1 were modelled. The numerical solutions reproduce the most spectacular features observed in the central part of the plerions: toroidal structure and jet‐like features. A comparison of the solutions with the observations confirms that magnetization of the wind from a pulsar in the Crab nebula is of the order of 3 × 10−3. The plasma flow in the nebula is variable. The variability has different time‐scales. Non‐periodic 2–3 yr scale variations are superimposed on the quasi‐periodical variations with period ∼40 yr. An increase of the wind's magnetization results in a decrease of the size of the synchrotron nebula. The size of the Vela nebula can be reproduced provided that the wind from Vela is more highly magnetized then the wind from Crab. Nevertheless, the magnetization of the wind from the Vela pulsar is most likely below 0.1.

The Evolution and Structure of Pulsar Wind Nebulae

“…As its free-flowing equatorial wind encounters the more slowly-expanding nebula, a termination shock is formed. Particles accelerated at the shock form a toroidal structure, while some of the flow is collimated along the rotation axis, possibly contributing to the formation of jet-like structures (Bogovalov et al 2005). These structures generate synchrotron radiation that is observed most readily in the X-ray band ( Fig.…”

HESS Observations of Pulsar Wind Nebulae

“…Although electrons and positrons from magnetospheric electromagnetic cascades escape with relatively low energy from the pulsar light cylinder, where the ratio σ L of electromagnetic energy density to particle energy density must be much larger than unity (σ L ∼ 10 4 for the Crab pulsar [22] this σ parameter must reduce drastically beyond the light cylinder for two reasons: (i) [65] have shown that the Crab pulsar's radio pulses would have been smeared unless the Lorentz factor of the e ± wind exceeds 10 4 ; (ii) Observations at the pulsar wind shock indicate that this ratio must have reduced to σ ∼ 3 × 10 −3 for the Crab [44,17], but in the range 0.01 to 0.1 for the Vela PWN shock [59,17]. The reader is referred to [11] for a review of this particle energization process.…”

“…The magnetic compression ratio 1 < κ < 3 [44] depends on the strength of this relativistic shock (and hence σ). For strong shocks (σ ≪ 1) we have κ ∼ 3, whereas κ ∼ 1 for weaker Vela-like shocks [44], where σ ∼ 0.01 to 0.1 [59,17]. The expression for the maximum particle energy for remnants with field strengths weaker than the Crab (i.e.…”

“…Assuming that the cocoon is still expanding under its own pressure, a perpendicular field component is expected to be maintained by virtue of Eqn (17), so that Eqn (19) with f ≪ 1 for Ωτ ≪ 1 or Ωτ ≫ 1 is expected to hold, which protects the integrity of this PWN against diffusive escape. Replacing the time T − T c with Eqn (26) in the diffusion equation, the electron energy cancels, so that the angular spread due to diffusion at a distance of d = 0.3 kpc can be written as…”

Unveiling the magnetic structure of VHE SNRs/PWNe with XIPE, the x-ray imaging-polarimetry explorer

“…Detailed morphological studies with Chandra revealed a complex structure of PWNe, such as, e.g., the torus-plus-jet structure in the Crab Nebula [7]. In general, young pulsars show an axial symmetry around what is believed to be the pulsar rotation axis [8,9,10,11]. Spatially-resolved measurements by XIPE will determine the magnetic field orientation and the level of turbulence in the torus, the jet, and at various distances from the pulsar.…”