Planetary and stellar auroral magnetospheric radio emission

A variety of astrophysical radio emissions have been identified to date in association with non-uniform magnetic fields and accelerated particle streams [1]. Such sources are spectrally well defined and for the planetary cases [1,2] show a high degree of extraordinary (X-mode) polarisation within the source region. It is now widely accepted that these emissions are generated by an electron cyclotron-maser instability driven by a horseshoe shaped electron velocity distribution. Although the generation mechanism is well established, a satisfactory explanation does not yet exist for the observed field aligned beaming of the radiation out-with the source region [2]. In the current context, the results of PiC simulations will be presented investigating the spatial growth of the horseshoe-maser instability in an unbounded interaction geometry, with a view to studying the wave vector of emission, spectral properties and RF conversion efficiency. In particular, the potential for backward-wave coupling is investigated as a viable precursor to a model of upward refraction and field-aligned beaming of the radiation [3].\\[4pt] [1] A.P. Zarka, Advances in Space Research, 12, pp. 99 (1992).\\[0pt] [2] R.E. Ergun et al., Astrophys. J., 538, pp. 456 (2000)\\[0pt] [3] J.D. Menietti et al., J. Geophys. Res., 116, A12219 (2011).