Absence of hot gas within the Wolft-Rayet Bubble around WR16

TL;DR

This study analyzes XMM-Newton data of the WR16 nebula, finding no diffuse X-ray emission and setting upper limits on its luminosity and electron density, contributing to understanding of hot gas presence in Wolf-Rayet bubbles.

Contribution

First X-ray upper limits for WR16's nebula, showing absence of hot gas, and providing constraints on electron density and thermal structure in Wolf-Rayet bubbles.

Findings

No diffuse X-ray emission detected in WR16 nebula.

Upper limit on X-ray luminosity is 7.4x10^{32} erg s^{-1}.

Electron density of hot gas is less than 0.6 cm^{-3}.

Abstract

We present the analysis of XMM-Newton archival observations towards the Wolf-Rayet (WR) bubble around WR16. Despite the closed bubble morphology of this WR nebula, the XMM-Newton observations show no evidence of diffuse emission in its interior as in the similar WR bubbles NGC6888 and S308. We use the present observations to estimate a 3-\sigma upper limit to the X-ray luminosity in the 0.3-1.5 keV energy band equal to 7.4x10^{32} erg s^{-1} for the diffuse emission from the WR nebula, assuming a distance of 2.37 kpc. The WR nebula around WR16 is the fourth observed by the current generation of X-ray satellites and the second not detected. We also examine FUSE spectra to search for nebular O VI absorption lines in the stellar continuum of WR16. The present far-UV data and the lack of measurements of the dynamics of the optical WR bubble do not allow us to confirm the existence of a conductive layer of gas at T~3x10^5 K between the cold nebular gas and the hot gas in its interior. The present observations result in an upper limit of n_e < 0.6 cm^-3 on the electron density of the X-ray emitting material within the nebula.