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The Vela supernova remnant displays several ejecta, which are fragment-likefeatures protruding beyond the front of its primary blast shock wave. Theyappear to be "shrapnel", bowshock-shaped relics of the supernova explosion. Oneof these pieces of shrapnel (A), located in the northeastern edge of theremnant, is peculiar because its X-ray spectrum exhibits a high Si abundance,in contrast to the other observed ejecta fragments, which show enhanced O, Ne,and Mg abundances. We present the analysis of another fragment located oppositeto shrapnel A with respect to the center of the shell, in the southwesternboundary of the remnant, named shrapnel G. We thoroughly analyzed a dedicatedXMM-Newton observation of shrapnel G by producing background-subtracted andexposure-corrected maps in different energy ranges, which we complemented witha spatially resolved spectral analysis of the X-ray emission. The fragmentpresents a bowshock-like shape with its anti-apex pointing to the center of theremnant. Its X-ray spectrum is best fit by a thermal plasma out of equilibriumof ionization with low O and Fe, roughly solar Ne and Mg, and a significantlyhigh Si abundance, which is required to fit a very clear Si line at ~1.85 keV.Its chemical composition and spectral properties are compatible with those ofshrapnel A, which is located on the opposite side of the remnant. As aconsequence of the nucleosynthesis, pieces of Si-rich shrapnel are expected tooriginate in deeper layers of the progenitor star compared to ejecta withlower-Z elements. A high velocity and density contrast with respect to thesurrounding ejecta are necessary to make shrapnel A and G overtake the forwardshock. The line connecting shrapnel A and G crosses almost exactly theexpansion center of the remnant, strongly suggesting a Si-rich jet-counterjetstructure, reminiscent of that observed in the young remnant Cas A.

Indications of a Si-rich bilateral jet of ejecta in the Vela SNR observed with XMM-Newton