Bullets in a Core‐Collapse Supernova Remnant: The Vela Remnant

We use two-dimensional hydrodynamical simulations to investigate the properties of dense ejecta clumps (bullets) in a core-collapse supernova remnant, motivated by the observation of protrusions probably caused by clumps in the Vela supernova remnant. The ejecta, with an inner flat and an outer steep power-law density distribution, were assumed to freely expand into an ambient medium with a constant density, ~0.1 H atoms cm -3 for the case of Vela. At an age of 10 4 yr, the reverse shock front is expected to have moved back to the center of the remnant. Ejecta clumps with an initial density contrast χ ~ 100 relative to their surroundings are found to be rapidly fragmented and decelerated. In order to cause a pronounced protrusion on the blast wave, as observed in the Vela remnant, χ ~ 1000 may be required. In this case, the clump should be near the inflection point in the ejecta density profile, at an ejecta velocity ~3000 km s -1 . These results apply to moderately large clumps; smaller clumps would require an even larger density contrast. Clumps can create ring structure in the shell of the Vela remnant, and we investigate the possibility that RX J0852-4622, an apparent supernova remnant superposed on Vela, is actually part of the Vela shell. Radio observations support this picture, but the possible presence of a compact object argues against it. The Ni bubble effect or compression in a pulsar wind nebula are possible mechanisms to produce the clumping.