X-ray emission from the wolf-rayet bubble s 308

The Wolf-Rayet (WR) bubble S308 around the WR star HD50896 is one of the only two WR bubbles known to possess X-ray emission. We present XMM-Newton observations of three fields of this WR bubble that, in conjunction with an existing observation of its northwest quadrant, map most of the nebula. The X-ray emission from S308 displays a limb-brightened morphology, with a central cavity 22′ in size and a shell thickness of 8′. This X-ray shell is confined by the optical shell of ionized material. The spectrum is dominated by the He-like triplets of N VI at 0.43keV and O VII at 0.57keV, and declines toward high energies, with a faint tail up to 1keV. This spectrum can be described by a two-temperature optically thin plasma emission model (T ₁ 1.1 × 10⁶K, T ₂ 13 × 10 ⁶K), with a total X-ray luminosity 2 × 10³³ergs ^-1 at the assumed distance of 1.5kpc.