Cosmic rays V. The nonthermal radio emission of the old nova GK Per - a signature of hadronic interactions?

Using the model of particle acceleration in shocks in stellar winds developed by Biermann (1993) and Biermann and Cassinelli (1993) we demonstrate that the nonthermal radio emission spectrum from the cataclysmic variable binary star GK Per can be interpreted consistently. We propose that the radio spectrum results from hadronic secondary electrons/positrons, which, in the optically thin case, give a characteristic radio spectrum with a spectral index of +1/3 below a maximum and, for a strong shock in a wind slow compared to the shock speed, of -0.7 above the maximum. We test the proposed concept for consistency with the radio data for OB and Wolf Rayet stars as well as radiosupernovae. There is some evidence that this process is important for the radio emission from active galactic nuclei, both in compact and extended emission. We argue that such a radio spectrum is a unique characteristic for hadronic interactions.