Radio SED of HD 93129A observed in May 2019, measured from the RACS-low (May 6th) and ATCA images (May 10th, this work). The solid lines are the total (absorption-corrected) SEDs, whereas the dashed-dotted lines are the total free–free emission from the combined stellar winds. Top panel: exploration of the impact of the wind volume filling factor f and the magnetic field prescription. The dashed lines show the SEDs calculated without including the frozen-in conditions where the shocked fluid becomes transonic. Bottom panel: exploration of the impact of the magnetic field strength (defined via the parameter η_B; Sect. 5.2). The dotted lines represent the unabsorbed synchrotron emission.