The Peculiar Ejecta Rings in the O-Rich Supernova Remnant Puppis A: Evidence of a Binary Interaction?

Near the center of the Puppis A supernova remnant a series of nested, optically emitting rings of high-velocity ejecta (known as "the Swirl") were identified several decades ago by Winkler et al. To date, no follow-up observations of these rings have been published, and their physical origin has remained a mystery. We present results of integral field spectroscopy of the Swirl using the Wide Field Integral Spectrograph on the 2.3 m telescope at Siding Spring Observatory in Australia. The outermost ring exhibits a nitrogen-rich spectrum blueshifted to 1350 km s-1, with smaller blueshifted rings within the first exhibiting mostly oxygen-rich spectra moving at 1000 and 750 km s-1. The structures are connected by material of intermediate velocity and variable composition, including sulfur-rich material. The Swirl is turbulent and shock-excited, and contains as much as 0.5 M circle dot of metal-rich material. The chemical composition and exclusively blueshifted radial velocities of the Swirl are consistent with progressively deeper nucleosynthetic layers in a massive progenitor star. We suggest the possibility that the Swirl marks a "funnel" carved into the supernova ejecta by a close, massive binary companion at the moment of explosion.