RCW 86: A TYPE Ia SUPERNOVA IN A WIND-BLOWN BUBBLE

Abstract

We report results from a multi-wavelength analysis of the Galactic SNR RCW\n86, the proposed remnant of the supernova of 185 A.D. We report new infrared\nobservations from {\\it Spitzer} and {\\it WISE}, where the entire shell is\ndetected at 24 and 22 $\\mu$m. We fit the infrared flux ratios with models of\ncollisionally heated ambient dust, finding post-shock gas densities in the\nnon-radiative shocks of 2.4 and 2.0 cm$^{-3}$ in the SW and NW portions of the\nremnant, respectively. The Balmer-dominated shocks around the periphery of the\nshell, large amount of iron in the X-ray emitting ejecta, and lack of a compact\nremnant support a Type Ia origin for this remnant. From hydrodynamic\nsimulations, the observed characteristics of RCW 86 are successfully reproduced\nby an off-center explosion in a low-density cavity carved by the progenitor\nsystem. This would make RCW 86 the first known case of a Type Ia supernova in a\nwind-blown bubble. The fast shocks ($> 3000$ km s$^{-1}$) observed in the NE\nare propagating in the low-density bubble, where the shock is just beginning to\nencounter the shell, while the slower shocks elsewhere have already encountered\nthe bubble wall. The diffuse nature of the synchrotron emission in the SW and\nNW is due to electrons that were accelerated early in the lifetime of the\nremnant, when the shock was still in the bubble. Electrons in a bubble could\nproduce gamma-rays by inverse-Compton scattering. The wind-blown bubble\nscenario requires a single-degenerate progenitor, which should leave behind a\ncompanion star.\n