The propeller driven pulsar-like spin-down and non-thermal emission in the nova-like variable star AE Aquarii

[摘要] English: The nova-like variable AE Aquarii consists of a fast rotating magnetized white dwarf, orbiting a late-type main sequence companion star. It is the most enigmatic among cataclysmic variables, and perhaps the best laboratory to study the physics of accretion and related phenomena, due to its multi-wavelength nature and unique flaring activity. The system is in an accretor-propeller state and most of its properties are associated with the propeller process. Using data observed contemporaneously with Chandra and Swift, the UV and X-ray properties of AE Aquarii have been studied. It is shown that the X-ray emission below 10 keV is predominantly soft and characterized by flares and emission lines. The spectra can be reproduced by multicomponent thermal emission models, and the time-averaged X-ray luminosity is determined to be LX 1031 erg s�?. The thermal soft X-ray emission (below 10 keV) is modelled in terms of plasma heating at the magnetospheric radius, where accretion flow from the secondary star interacts with the magnetosphere of the white dwarf. Both UV and X-ray emission are pulsed at the spin period of the white dwarf. The recently detected hard X-ray emission in AE Aquarii (above 10 keV), with a luminosity of LX,hard 6 5 × 1030 erg s�?, shows a non-thermal nature, possible synchrotron emission of high energy electrons in the white dwarf magnetosphere. It is proposed that these electrons are accelerated by large field aligned potentials of V > 1012 V, a process common in the magnetospheres of fast rotating neutron stars, or pulsars. This places AE Aquarii in a unique category with respect to most members of cataclysmic variables. The ratio of the observed hard X-ray luminosity to the spin-down luminosity of the white dwarf in AE Aquarii lies in the range 0.01-0.1 %, which is the same as observed from young rotation-powered neutron stars in the 2-10 KeV range. In this regard, a pulsar-like model is appropriate to explain the origin of the observed non-thermal hard X-ray emission in AE Aquarii.

[发布机构] University of the Free State