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

Abstract

We use two-dimensional hydrodynamical simulations to investigatethe properties of dense ejecta clumps (bullets) in a core-collapsesupernova remnant, motivated by the observation of protrusions probablycaused by clumps in the Vela supernova remnant. The ejecta, withan inner flat and an outer steep power-law density distribution,were assumed to freely expand into an ambient medium with a constantdensity, ~0.1 H atoms cm-3 for the case of Vela. At an age of104 yr, the reverse shock front is expected to have moved back tothe center of the remnant. Ejecta clumps with an initial densitycontrast chi~100 relative to their surroundings are found to be rapidlyfragmented and decelerated. In order to cause a pronounced protrusionon the blast wave, as observed in the Vela remnant, chi~1000 maybe required. In this case, the clump should be near the inflectionpoint in the ejecta density profile, at an ejecta velocity ~3000km s-1. These results apply to moderately large clumps;smaller clumps would require an even larger density contrast. Clumpscan create ring structure in the shell of the Vela remnant, and weinvestigate the possibility that RX J0852-4622, an apparent supernovaremnant superposed on Vela, is actually part of the Vela shell. Radioobservations support this picture, but the possible presence of a compactobject argues against it. The Ni bubble effect or compression in apulsar wind nebula are possible mechanisms to produce the clumping.