X-rays from the oxygen-type Wolf-Rayet binary WR30a

TL;DR

WR30a is a highly X-ray luminous oxygen-type Wolf-Rayet binary with a complex spectrum featuring two broad peaks, requiring a two-component model, but the exact X-ray emission mechanism remains uncertain.

Contribution

This study provides the first detailed X-ray spectral analysis of WR30a, revealing its high luminosity and spectral complexity, and discusses possible emission mechanisms.

Findings

WR30a has an X-ray luminosity > 10^{34} erg/s.

The spectrum shows two broad peaks at 1-2 keV and 5-7 keV.

The emission mechanism remains unclear, fitting both thermal and nonthermal models.

Abstract

We present an analysis of XMM-Newton X-ray data of WR30a (WO+O), a close massive binary that harbours an oxygen-rich Wolf-Rayet star. Its spectrum is characterized by the presence of two well-separated broad peaks, or `bumps', one peaking at energies between 1 and 2 keV and the other between 5 and 7 keV. A two-component model is required to match the observed spectrum. The higher energy spectral peak is considerably more absorbed and dominates the X-ray luminosity. For the currently accepted distance of 7.77 kpc, the X-ray luminosity of WR30a is L_X > 10^{34} erg s^{-1}, making it one of the most X-ray luminous WR+O binary amongst those in the Galaxy with orbital periods less than ~20 d. The X-ray spectrum can be acceptably fitted using either thermal or nonthermal models, so the X-ray production mechanism is yet unclear.