An X-ray study of the remnant of SN 185 A.D

High-resolution X-ray maps obtained with the Einstein Observatory of the supernova remnant RCW 86 are presented. Analysis of the spatial and spectral properties of the remnant yield a total X-ray emitting mass of not greater than about 5 solar masses and a surrounding mean interstellar density of about 0.3/cu cm. A revision of the generally accepted distance of 2.5 kpc downward to not greater than about 1 kpc is strongly suggested by the data. The diameter (about 13 pc) and X-ray plasma temperature (about 1 keV) are consistent with the identification of the remnant with the supernova of 185 A.D. The observed apparent magnitude of SN 185 coupled with the new distance, the implied explosion energy and ejected mass derived from a Sedov analysis, and the lack of any compact remnant are all characteristic of a Type I event.