RCW 86: A Type Ia Supernova in a Wind-Blown Bubble

TL;DR

This study presents multi-wavelength observations and hydrodynamic modeling of the RCW 86 supernova remnant, suggesting it is a Type Ia supernova remnant expanding in a wind-blown bubble, a first such case.

Contribution

It provides the first evidence of a Type Ia supernova remnant in a wind-blown bubble through combined observational and simulation data.

Findings

Infrared flux ratios indicate post-shock densities of 2.4 and 2.0 cm$^{-3}$.

Hydrodynamic models reproduce observed features with an off-center explosion in a low-density cavity.

The remnant's characteristics support a single-degenerate progenitor scenario.

Abstract

We report results from a multi-wavelength analysis of the Galactic SNR RCW 86, the proposed remnant of the supernova of 185 A.D. We report new infrared observations from {\it Spitzer} and {\it WISE}, where the entire shell is detected at 24 and 22 $\mu$m. We fit the infrared flux ratios with models of collisionally heated ambient dust, finding post-shock gas densities in the non-radiative shocks of 2.4 and 2.0 cm$^{-3}$ in the SW and NW portions of the remnant, respectively. The Balmer-dominated shocks around the periphery of the shell, large amount of iron in the X-ray emitting ejecta, and lack of a compact remnant support a Type Ia origin for this remnant. From hydrodynamic simulations, the observed characteristics of RCW 86 are successfully reproduced by an off-center explosion in a low-density cavity carved by the progenitor system. This would make RCW 86 the first known case of a Type Ia supernova in a wind-blown bubble. The fast shocks ($> 3000$ km s$^{-1}$) observed in the NE are propagating in the low-density bubble, where the shock is just beginning to encounter the shell, while the slower shocks elsewhere have already encountered the bubble wall. The diffuse nature of the synchrotron emission in the SW and NW is due to electrons that were accelerated early in the lifetime of the remnant, when the shock was still in the bubble. Electrons in a bubble could produce gamma-rays by inverse-Compton scattering. The wind-blown bubble scenario requires a single-degenerate progenitor, which should leave behind a companion star.