Absence of hot gas within the Wolft-Rayet Bubble around WR16
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-σ upper limit to the X-ray luminosity in the 0.3-1.5 keV energy band equal to 7.4x1032 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~3x105 K between the cold nebular gas and the hot gas in its interior. The present observations result in an upper limit of ne < 0.6 cm-3 on the electron density of the X-ray emitting material within the nebula.
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