X-rays from the oxygen-type Wolf-Rayet binary WR 30a

Abstract

We present an analysis of XMM-Newton X-ray data of WR 30a (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 WR 30a is L_X > 10³⁴ erg s^-1, making it one of the most X-ray luminous WR+O binaries amongst those in the Galaxy with orbital periods less than ∼20 d. The X-ray spectrum can be acceptably fitted using either thermal or non-thermal models, so the X-ray production mechanism is yet unclear.