Polarization and Structure of the Crab Nebula : Proceedings of the 23rd IAU Colloquium

Abstract

Present knowledge of the optical, radio and X -ray polarization of the Crab is reviewed and discussed as it bears on the structure of the magnetic field, time scales in the nebula, and relations between nebula and pulsar. Not as much high -resolution polarimetry has been done on the Crab as might have been expected. Loops of field and a large -scale structure can be recognized, but it is not known whether the fields generally are smooth or chaotic on a small scale. Field lines tend to curl around the filaments. The large angular size of the X -ray source poses a difficulty to conventional theory. The form of the nebula does not single out the pulsar as its source, and the exact relation between pulsar and nebula is uncertain. The wave -field or "synchro- Compton" interpretation of the continuum emission is erroneous but has led to interesting observations of circular polarization. Circular polarization of the ordinary synchrotron radiation might be observable in the radio band. Magnetic flux may have been generated in the nebula by winding of lines around the rotating pulsar. Polaroid photographs then suggest that the pulsar rotation axis is roughly NW -SE, but confirmation is lacking.