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The recently discovered colliding-wind binary (CWB) Apep has been shown toemit luminously from radio to X-rays, with the emission driven by a binarycomposed of two Wolf-Rayet (WR) stars of one carbon-sequence (WC8) and onenitrogen-sequence (WN4-6b). Mid-infrared imaging revealed a giant spiral dustplume that is reminiscent of a pinwheel nebula but with additional featuresthat suggest Apep is a unique system. We have conducted observations with theAustralian Long Baseline Array to resolve Apep's radio emission onmilliarcsecond scales, allowing us to relate the geometry of the wind-collisionregion to that of the spiral plume. The observed radio emission shows abow-shaped structure, confirming its origin as a wind-collision region. Theshape and orientation of this region is consistent with being originated by thetwo stars and with being likely dominated by the stronger wind of the WN4-6bstar. This shape allowed us to provide a rough estimation of the opening angleof $\sim 150^\circ$ assuming ideal conditions. The orientation and openingangle of the emission also confirms it as the basis for the spiral dust plume.We also provide estimations for the two stars in the system to milliarcsecondprecision. The observed radio emission, one order of magnitude brighter andmore luminous than any other known non-thermal radio-emitting CWB, confirms itis produced by an extremely powerful wind collision. Such a powerfulwind-collision region is consistent with Apep being a binary composed of two WRstars, so far the first unambiguously confirmed system of its kind.

AU-scale radio imaging of the wind collision region in the brightest and most luminous non-thermal colliding wind binary Apep