85-GHz BIMA observations of the double-hotspot radio galaxy 3C20

We present 85-GHz observations of the archetypal double-hotspot radio source 3C20 made with the BIMA millimetre array. The resolution of BIMA allows us to separate the two components of the eastern hotspot. By comparing the BIMA observations with existing VLA data, we show that the spectra of the two hotspot components are very similar, despite the clear differences in their radio structure and their wide separation. We discuss the implications for models of double hotspot formation. Weak emission from the lobes of 3C20 is detected at 85 GHz, at a level consistent with the predictions of standard spectral ageing models.