The inner knot of the Crab nebula

Abstract

We model the inner knot of the Crab Nebula as a synchrotron emission coming from the non-spherical MHD termination shock of relativistic pulsar wind. The post-shock flow is mildly relativistic; as a result the Doppler-beaming has a strong impact on the shock appearance. The model can reproduce the knot location, size, elongation, brightness distribution, luminosity and polarization provided the effective magnetization of the section of the pulsar wind producing the knot is low, $\sigma \le 1$. In the striped wind model, this implies that the striped zone is rather wide, with the magnetic inclination angle of the Crab pulsar $\ge 45^{\circ }$; this agrees with the previous model-dependent estimate based on the gamma-ray emission of the pulsar. We conclude that the tiny knot is indeed a bright spot on the surface of a quasi-stationary magnetic relativistic shock and that this shock is a site of efficient particle acceleration. On the other hand, the deduced low magnetization of the knot plasma implies that this is an unlikely site for the Crab's gamma-ray flares, if they are related to the fast relativistic magnetic reconnection events.

16 pages, 17 figures

References in corpus (5)

• Gamma-ray flares from the Crab Nebula
• Discovery of Powerful Gamma-Ray Flares from the Crab Nebula
• Ab-initio pulsar magnetosphere: three-dimensional particle-in-cell simulations of oblique pulsars
• Characterization of the Inner Knot of the Crab: The Site of the Gamma-ray Flares?
• On the Implications of Recent Observations of the Inner Knot in the Crab Nebula

Cited by in corpus (17)

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• Interpreting Crab Nebula synchrotron spectrum: two acceleration mechanisms
• Particle acceleration in explosive relativistic reconnection events and Crab Nebula gamma-ray flares
• Particle acceleration in explosive relativistic reconnection events and Crab Nebula gamma-ray flares
• A recent change in the optical and γ-ray polarization of the Crab nebula and pulsar
• Turbulent magnetic relaxation in pulsar wind nebulae
• The imprint of pulsar parameters on the morphology of Pulsar Wind Nebulae
• Modelling Jets, Tori and Flares in Pulsar Wind Nebulae
• Detection of Small Flares from the Crab Nebula with Fermi-LAT
• On the Implications of Recent Observations of the Inner Knot in the Crab Nebula
• Magnetic loading of magnetars' flares
• Multidimensional relativistic MHD simulations of Pulsar Wind Nebulae: dynamics and emission
• Early GRB afterglows from reverse shocks in ultra-relativistic long-lasting winds
• Fermi Large Area Telescope Observations of the Fast-dimming Crab Nebula in 60-600 MeV
• Time-Dependent Electron Acceleration in Pulsar-Wind Termination Shocks: Application to the 2011 April Crab Nebula Gamma-Ray Flare