X-ray emission from the Wolf-Rayet bubble S308

TL;DR

This study presents XMM-Newton X-ray observations of the Wolf-Rayet bubble S 308, revealing its limb-brightened morphology, spectral properties, and plasma temperatures, contributing to understanding WR bubble X-ray emissions.

Contribution

First detailed X-ray mapping of S 308 using multiple observations, characterizing its morphology and plasma properties with a two-temperature model.

Findings

X-ray emission shows limb-brightened morphology

Spectrum dominated by He-like triplets of NIV and OVII

Total X-ray luminosity approximately 2x10^33 erg/s

Abstract

The Wolf-Rayet (WR) bubble S 308 around the WR star HD 50896 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 S 308 displays a limb-brightened morphology, with a central cavity ~22 arcmin in size and a shell thickness of ~8 arcmin. This X-ray shell is confined by the optical shell of ionized material. The spectrum is dominated by the He-like triplets of NIV at 0.43 keV and OVII at 0.57 keV, and declines towards high energies, with a faint tail up to 1 keV. This spectrum can be described by a two-temperature optically thin plasma emission model (T1 ~ 1.1x10^6 K, T2 ~ 13x10^6 K), with a total X-ray luminosity ~2x10^33 erg/s at the assumed distance of 1.5 kpc.