Norton, A. J.; Beardmore, A. P. and Taylor, P.
On the interpretation of intermediate polar X-ray power spectra.
Monthly Notices of the Royal Astronomical Society, 280(3)
The authors discuss the various emission and attenuation components that contribute to the overall X-ray signal produced by an intermediate polar. This description is then used to construct an algebraic expression that represents the complex modulation of the X-ray lightcurve, in terms of a number of parameters that describe the emission and attenuation properties of the system. The authors expand this expression in terms of its individual frequency components and so determine the amplitudes and phases that would be observed at a range of spin and orbital harmonic and sideband frequencies in the X-ray power spectrum of a given source. The authors conclude from this that a vast range of frequency components are to be expected in the X-ray lightcurve of an intermediate polar that accretes via a combination of an accretion disc and an accretion stream on to two asymmetric regions in the vicinity of the magnetic poles. For systems in which the accretion process is less complex, the power spectra are correspondingly simpler. The authors examine the X-ray power spectra of AO Psc, V1223 Sgr, FO Aqr and BG CMi obtained with Ginga and, where possible, with ROSAT. By considering these observed power spectra in the light of the model, the authors conclude that: there is an absorption site fixed in the orbital frame in all systems; AO Psc accretes solely via a disc; FO Aqr and BG CMi accrete via combinations of disc and stream; and the accretion mode in FO Aqr changed between 1988 and 1990.
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