A 3D Kinematic Study of the Northern Ejecta "Jet" of the Crab Nebula
  We present [O III] 4959,5007 emission line spectra (FWHM = 40 km/s) of the Crab Nebula's northern ejecta `jet'. These data, along with a recent [O III] image of the Crab, are used to build 3-dimensional models of the jet and adjacent remnant nebulosity to better understand the jet's properties and possible formation. We find that the jet's radial velocities range from -190 to +480 km/s with transverse velocities from 1600 to 2650 km/s from base to tip. The jet appears virtually hollow in [O III] emission with the exception of some material at the jet's base where the it connects with the remnant. Our 3D reconstructions indicate that the jet is elliptical in shape and slightly funnel-like rather than a straight cylindrical tube as previously thought. At the base of the jet we find evidence for a significant opening or "channel" in the Crab's main nebula shell. Our analysis of the jet's expansion properties and location supports the theory that the jet may simply represent the highest velocity component of the Crab's N-S bipolar expansion. 
Christine S. Black and Robert A. Fesen
astro-ph.HE