Magnetic fields in the «jet» of the Crab Nebula

The Very Large Array has been used to map the 20 cm intensity and polarization distributions in the Crab Nebula with better resolution (about 4 arcsec) than achieved in previous radio observations. Lower resolution polarization observations at 6 cm are also reported. The radio emission from the jet is well correlated with its O III forbidden line emission but is highly polarized, testifying to a uniform magnetic field and an absence of internal Faraday depolarizing gas. The pressures of the cosmic rays and magnetic fields probably dominate that of the thermal material. The magnetic field in the base of the jet runs almost radially (with respect to the local edge or the center of the nebula) and appears to be slightly misaligned with the line-emitting walls. The jet seems to represent relativistic and thermal gases escaping radially outward through a hole in the filamentary shell. Such strictly radial motion can account for the magnetic field direction, the relative magnitudes of the jets' velocity components in and perpendicular to the plane of the sky, and the similar kinematic ages derived from these two components.