On the Implications of Recent Observations of the Inner Knot in the Crab Nebula

Abstract

Recent observations of the Crab Nebula (Rudy et al 2015) have maintained its reputation for high energy astrophysical enlightenment and its use as a testbed for theories of the behaviour of magnetized, relativistic plasma. In particular, new observations of the inner knot located 0.65" SE from the pulsar confirm that it is compact, elongated transversely to the symmetry axis and curved concave towards the pulsar. 60 percent polarization has been measured along the symmetry axis (Moran et al 2013). The knot does not appear to be involved in the gamma ray flares. The new observations both reinforce the interpretation of the knot as dissipation of the pulsar wind at a strong shock and challenge the details of existing models of this process. In particular, it is argued that the compactness, high polarization and curvature are difficult to reconcile with simple relativistic shock models. Alternative possibilities include deflection of the outflow ahead of the shock and spatial variation in which the knot is interpreted as a caustic. Some future observations are proposed and new theoretical investigations are suggested.

17 pages, 13 figures. Published in MNRAS

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Cited by in corpus (13)

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• 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
• The inner knot of the Crab nebula
• Multidimensional relativistic MHD simulations of Pulsar Wind Nebulae: dynamics and emission
• Early GRB afterglows from reverse shocks in ultra-relativistic long-lasting winds