Multifrequency observations of the Wolf-Rayet star WR 146: another colliding-wind binary?

We present the first high-spatial-resolution radio observations of the Wolf-Rayet star WR 146, obtained at 1.6 and 5 GHz with the MERLIN array. The 5-GHz observations resolve the source into two components separated by 116 ± 14 milliarcsecond (mas). The weaker (southern) source is identified as thermal emission arising from the stellar wind of the WR star and the stronger (northern) source, which is resolved with a diameter of 38 mas and a brightness temperature Tb ∼ 106 K, as non-thermal emission. New infrared and millimetre photometry of WR 146 is consistent with a stellar-wind origin for the southern radio component, and allows us to estimate the distance to the WR star to be 1.2 ±0.3 kpc. We also present a blue spectrum of WR 146, which shows evidence for absorption lines attributable to an OB-type companion to the WC6 star. In these respects, WR 146 is similar to the other Wolf-Rayet stars (WR 125 and 140) known to be non-thermal emitters. We suggest that the non-thermal emission arises from the interaction of the WR wind and that of its newly detected luminous companion. The observed size of the non-thermal radio-emitting region is consistent with that expected from colliding-wind theory. We estimate that the non-thermal emission is essentially unabsorbed by the stellar wind of the WR star, providing an unprecedented opportunity for studying colliding winds.