2005A&A...440..743B

We present results of high-resolution radio continuum observations towards the binary star WR 21a (Wack 2134) obtained with the Australia Telescope Compact Array (ATCA) at 4.8 and 8.64GHz. We detected the system at 4.8GHz (6cm) with a flux density of 0.25±0.06mJy and set an upper limit of 0.3mJy at 8.64GHz (3cm). The derived spectral index of α<0.3 (S_ν∝ν^α) suggests the presence of non-thermal emission, probably originating in a colliding-wind region. A second, unrelated radio source was detected ∼10" north of WR 21a at (RA, Dec)_J2000=(10^h25^m56.49^s, -57°48'34.4"), with flux densities of 0.36 and 0.55mJy at 4.8 and 8.64GHz, respectively, resulting in α=0.72. HI observations in the area are dominated by absorption against the prominent HII region RCW 49. Analysis of a complete set of archived X-ray observations of WR 21a confirms its strong variability but throws into doubt previous suggestions by Reig (1999) of a period of years for the system. Finally, we comment on the association with the nearby EGRET source 3EG J1027-5817.