  We follow up on our (Radhakrishnan & Deshpande, 2001: RD01) radically
different interpretation of the observed structures and morphologies in the
x-ray observations of the nebulae around young pulsars (PWNe). In our general
model for PWNe (RD01), originally motivated by the Chandra observations of the
Vela X-ray nebula, the bright arcs, the jet-like feature and the diffuse
components in such nebulae can be explained together in detail, wherein the
arcs are understood as traces of the particle beams from the two magnetic poles
at the shock front. We consider this as important evidence for collimated
particle beams from pulsars' magnetic poles. In this paper, we discuss the
variability in the features in the Vela X-ray nebula observed by Pavlov et al.
(2003), and assess the relevance and implication of our model to the
observations on the Crab and other remnants. Our basic picture after
incorporating the signatures of free precession of the central compact object
can readily account for the variability and significant asymmetries, including
the bent jet-like features, in the observed morphologies. The implications of
these findings are discussed.
