CCD OBSERVATIONS OF THE POLARIZATION OF THE CRAB-NEBULA

CCD observations are used to map the intensity distribution and polarization of the optical synchrotron radiation of the Crab Nebula. Our data indicate that the Crab Nebula has a large-scale magnetic field in which major variations generally occur over regions with sizes larger than 10″ (0.1 pc). However, in the vicinity of the Crab pulsar, the polarization shows structure on a scale of a few arcsec. We find evidence for a narrow depolarized channel extending from the pulsar to the region of the optical wisps in the synchrotron nebula. Our results also confirm previous studies which show that the magnetic vectors of polarization are predominantly oriented parallel to the edges of the "dark bays" in the outer regions of the visible synchrotron nebulosity. This supports the suggestion that these regions of the Nebula are wrapped in magnetic field lines, and are therefore deficient in electrons capable of emitting synchrotron radiation.