Observation of a pulsar wind: CCD polarimetry of the Crab Nebula

Stokes parameters have been extracted from CCD images of the Crab Nebula in polarized light and recombined to give images of the nebula in totally polarized light and totally unpolarized light. Images in totally polarized light show dominant emission in an hour-glass structure. Theoretical expectations on general grounds predict a predominantly azimuthal magnetic field about the pulsar spin axis. Synchrotron radiation from energetic electrons with a range of pitch angles ∼90°, when viewed off-axis, naturally produces an hour-glass radiation pattern. Much of the remaining structure: "scalloping" of the outer reaches of the synchrotron nebula about the edges and depolarization across the face of the nebula seems plausibly interpreted in terms of interaction with the filamentary structure. In effect, the filaments appear to form a conducting "cage" from which the pulsar wind is attempting to escape with the wind structure thereby "pooching" out between dense filaments.