Discovery of X-ray Emission from the Wolf-Rayet star WR142 of oxygen subtype

TL;DR

This paper reports the first detection of X-ray emission from the WO-type Wolf-Rayet star WR142, revealing hard X-ray spectra likely linked to magnetic activity and rapid rotation, providing new insights into the properties of evolved massive stars.

Contribution

It is the first to detect X-ray emission from a WO-type Wolf-Rayet star and explores potential mechanisms behind the hard X-ray spectrum, including magnetic activity and rapid rotation effects.

Findings

First X-ray detection from WO-type star WR142

X-ray luminosity is about 10^{-8} of bolometric luminosity

Hard X-ray spectrum suggests plasma temperature of ~100 MK

Abstract

We report the discovery of weak yet hard X-ray emission from the Wolf-Rayet (WR) star WR142 with the XMM-Newton X-ray telescope. Being of spectral subtype WO2, WR142 is a massive star in a very advanced evolutionary stage, short before its explosion as a supernova or gamma-ray burst. This is the first detection of X-ray emission from a WO-type star. We rule out any serendipitous X-ray sources within approx 1" of WR142. WR142 has an X-ray luminosity of L_X=7\times10^{30} erg/s, which constitutes only $\lsim 10^{-8}$ of its bolometric luminosity. The hard X-ray spectrum suggests a plasma temperature of about 100 MK. Commonly, X-ray emission from stellar winds is attributed to embedded shocks due to the intrinsic instability of the radiation driving. From qualitative considerations we conclude that this mechanism cannot account for the hardness of the observed radiation. There are no hints for a binary companion. Therefore the only remaining, albeit speculative explanation must refer to magnetic activity. Possibly related, WR142 seems to rotate extremely fast, as indicated by the unusually round profiles of its optical emission lines. Our detection implies that the wind of WR142 must be relatively transparent to X-rays, which can be due to strong wind ionization, wind clumping, or non-spherical geometry from rapid rotation.