Aims. We intend to establish the X-ray properties of Swift J0732.5-1331 and therefore confirm its status as an intermediate polar. Method. We analysed 36,240 s of X-ray data from RXTE. Frequency analysis was used to constrain temporal variations and
spectral analysis used to characterise the emission and absorption properties. Results. The X-ray spin period is confirmed to be 512.4(3) s with a strong first harmonic. No modulation is detected at the candidate orbital period of 5.6 h, but a coherent modulation is present at the candidate 11.3 h period. The spectrum is consistent with a 37 keV bremsstrahlung continuum with an iron line at 6.4 keV absorbed by an equivalent hydrogen column density of around 10^22 atoms cm^-2. Conclusions. Swift J0732-1331 is confirmed to be an intermediate polar.
We have used a model of magnetic accretion to investigate the accretion flows of magnetic cataclysmic variables. Numerical simulations demonstrate that four types of flow are possible: discs, streams, rings and propellers. The fundamental observable
determining the accretion flow, for a given mass ratio, is the spin-to-orbital period ratio of the system. If IPs are accreting at their equilibrium spin rates, then for a mass ratio of 0.5, those with Pspin/Porb < 0.1 will be disc-like, those with 0.1 < Pspin/Porb < 0.6 will be stream-like, and those with Pspin/Porb ~ 0.6 will be ring-like. The spin to orbital period ratio at which the systems transition between these flow types increases as the mass ratio of the stellar components decreases. For the first time we present evolutionary tracks of mCVs which allow investigation of how their accretion flow changes with time. As systems evolve to shorter orbital periods and smaller mass ratios, in order to maintain spin equilibrium, their spin-to-orbital period ratio will generally increase. As a result, the relative occurrence of ring-like flows will increase, and the occurrence of disc-like flows will decrease, at short orbital periods. The growing number of systems observed at high spin-to-orbital period ratios with orbital periods below 2h, and the observational evidence for ring-like accretion in EX Hya, are fully consistent with this picture.
