Spitzer Space Telescope Observations of the Magnetic Cataclysmic Variable AE Aquarii

The magnetic cataclysmic variable AE Aquarii hosts a rapidly rotating white dwarf that is thought to expel most of the material streaming onto it. Observations of AE Aqr have been obtained in the wavelength range 5-70 μm with the IRS, IRAC, and MIPS instruments on board the Spitzer Space Telescope. The spectral energy distribution reveals a significant excess above the K4 V spectrum of the donor star, with the flux increasing with wavelength above 12.5 μm. Superposed on the energy distribution are several hydrogen emission lines, identified as Pfα and Huα, Huβ, and Huγ. The infrared spectrum above 12.5 μm can be interpreted as synchrotron emission from electrons accelerated to a power-law distribution dN ∝ E-2.4 dE in expanding clouds, with an initial evolutionary timescale of seconds. However, too many components must then be superposed to explain satisfactorily both the mid-infrared continuum and the observed radio variability. Thermal emission from cold circumbinary material could contribute, but it requires a disk temperature profile intermediate between that produced by local viscous dissipation in the disk and that characteristic of a passively irradiated disk. Future high time resolution observations spanning the optical-to-radio regime could shed light on the acceleration process and the subsequent particle evolution.