Radio light curve of WR112 from VLA & ATCA

We report the first X-ray detections of the dusty WC+O binary system WR 112 from Chandra and Swift, alongside 27yr of Very Large Array/Australia Telescope Compact Array radio monitoring and new diffraction-limited Keck images. Because we view the nearly circular orbit almost edge-on, the colliding-wind zone alternates between heavy Wolf-Rayet wind self-absorption and near-transparent O-star wind foreground each 20yr orbit, producing phase-locked radio and X-ray variability.

This scenario leads to a prediction that the radio spectral index is flatter from a larger nonthermal contribution around the radio intensity maximum, which indeed was observed. Existing models that assume a single dust-expansion speed fail to reproduce the combined infrared (IR) geometry and radio light curve. Instead, we require an accelerating postshock flow that climbs from near-stationary to ~1350km/s in about one orbital cycle, naturally matching the IR spiral from 5" down to within 0.1", while also fitting the phase of the radio brightening.