Markwardt and Ogelman (1995) used ROSAT to reveal a 12 by 45 arcmin structure in 1 keV X rays around the Vela pulsar, which they interpret as a jet emanating from the pulsar. We here present an alternative view of the nature of this feature, namely that it consists of material from very deep inside the exploding star, close to the mass cut between material that became part of the neutron star and ejected material. The initial radial velocity of the inner material was lower than the bulk of the ejecta, and formed a bubble of slow, dense material that started expanding again due to heating by the young pulsar's spindown energy. The expansion is mainly in one direction, and to explain this we speculate that the pre-supernova system was a binary. The explosion caused the binary to unbind, and the pulsar's former companion crossed the bubble carving a lower density channel into the shell interior, puncturing the edge and greatly facilitating expansion along its path relative to other directions. If this is the case, we can estimate the current speed of the former binary companion and from this reconstruct the presupernova binary orbit. If follows that the exploding star was a helium star, hence that the supernova was of type Ib.
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