X-ray emission from the Wolf-Rayet bubble NGC 6888. II. XMM-Newton EPIC observations

TL;DR

This study uses deep XMM-Newton observations to map the hot gas in the Wolf-Rayet bubble NGC 6888, revealing temperature and composition variations that suggest uneven mixing processes within the nebula.

Contribution

First detailed spectral variation analysis of hot gas in NGC 6888, identifying inhomogeneities in temperature and nitrogen abundance.

Findings

Hot gas distribution aligns with previous Chandra observations.

X-ray emission is modeled by a two-temperature plasma with specific temperatures and luminosity.

Spectral variations indicate less efficient mixing of nebular material in certain regions.

Abstract

We present deep XMM-Newton EPIC observations of the Wolf-Rayet (WR) bubble NGC6888 around the star WR136. The complete X-ray mapping of the nebula confirms the distribution of the hot gas in three maxima spatially associated with the caps and northwest blowout hinted at by previous Chandra observations. The global X-ray emission is well described by a two-temperature optically thin plasma model $T_1$=1.4$\times$10$^{6}$ K, $T_{2}$=8.2$\times$10$^{6}$ K) with a luminosity of $L_{\mathrm{X}}$=7.8$\times$10$^{33}$ erg s$^{-1}$ in the 0.3--1.5 keV energy range. The rms electron density of the X-ray-emitting gas is estimated to be $n_\mathrm{e}$=0.4 cm$^{-3}$. The high-quality observations presented here reveal spectral variations within different regions in NGC6888, which allowed us for the first time to detect temperature and/or nitrogen abundance inhomogeneities in the hot gas inside a WR nebula. One possible explanation for such spectral variations is that the mixing of material from the outer nebula into the hot bubble is less efficient around the caps than in other nebular regions.