The diamagnetic blob propeller in AE Aquarii and non‐thermal radio to mid‐infrared emission

This paper presents a qualitative investigation of the propeller mechanism in AE Aquarii within the framework of the magnetohydrodynamic (MHD) interaction between the fast rotating magnetosphere of the white dwarf and a blobby mass flow stream from the secondary star. It has been shown that the denser part of the mass flow can penetrate the fast rotating magnetosphere of the white dwarf to the circularization radius, before it is ejected from the system. It has been shown that the total MHD power dissipated on a volume of material equivalent to an orbiting ring of cross‐sectional radius R stream ∼ 10 9 cm , at the circularization radius, is P MHD ∼ 10 34  erg s −1 , which is of the same order of magnitude as the inferred spin‐down power of the white dwarf. Mixing of the magnetospheric field with a turbulent gas stream due to turbulent diffusion and Kelvin–Helmholtz instabilities, creating magnetic vortices in the flow, results in a transfer of mechanical energy to the stream, accelerating it like a slingshot to velocities exceeding the escape velocity over time‐scales far too short for viscous spreading of the material into a disc. The diffusion of the field into the turbulent gas probably results in stripping of the magnetospheric field through fast reconnection as a result of the huge differential rotation, resulting in the creation of magnetized plasma clouds with fields of B cloud ≥ 300 G . It has been shown that the interaction of the white dwarf field with the magnetized blob can accelerate electrons to energies of at least ε e ∼ 130 MeV within the dominant energy‐loss time‐scales, which is high enough to account for the maximum electron energies of ε max ∼ 80 MeV , inferred from the latest detection of possible non‐thermal emission at frequencies ν∼ 17 000 GHz and 25 000 GHz, using the Keck I Telescope in Hawaii. It has been shown that the efficiency of the MHD propeller in converting thermal electrons to relativistic electrons, energetic enough to drive the total observed non‐thermal emission in AE Aquarii, is probably of the order of ∼0.1 per cent. This is consistent with the ratio ( β∼ 0.1 per cent) of the total observed radio to mid‐infrared synchrotron emission to the total spin‐down power of the white dwarf. Based upon energy arguments, it has been shown that magnetized synchrotron‐emitting clouds with fields of B eq ∼ 300 G , which is similar to the magnetospheric field at the main interaction zone, i.e. the circularization radius, can confine a population of relativistic electrons that are able to power the total observed non‐thermal radio to mid‐infrared emission with luminosity L R–IR ∼ 10 31  erg s −1 .