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The X-ray light curves of AM Herculis systems

1988; Oxford University Press; Volume: 235; Issue: 2 Linguagem: Inglês

10.1093/mnras/235.2.433

1365-2966

J. M. Hameury, A. R. King,

Astrophysical Phenomena and Observations

We reconsider the X-ray light curves of AM Herculis systems using the inhomogeneous accretion picture suggested by Kuijpers & Pringle and developed by Frank, King & Lasota. We show that the soft X-ray light curves of AM Her (and other systems) at both ‘normal’ and ‘anomalous’ epochs can be readily understood: the form depends on the separation and number of dense, soft X-ray producing blobs accreting instantaneously. In the anomalous state of AM Her, this number is only ∼15, falling on a sparsely populated accretion zone; the individual footpoints are seen in soft X-rays as protruding splashes and give rapid transitions from the low to high flux levels as the accretion zone (<10−2 of the white dwarf surface) rotates into view. The high level occupies ∼50 per cent of the cycle, as observed. In the normal state, there are many more dense blobs, and the curves become quasi-sinusoidal. In all cases, there is a strict hierarchy between the instantaneous area Aacc accreting dense blobs, the effective area Aeff radiating most of the accretion luminosity as soft X-rays, the total zone area Azone over which the blobs are scattered, and the white dwarf surface area 4πR2, namely |$A_\text{acc}\ll A_\text{eff}\lt,\enspace\ll A_\text{zone}\ll 4\pi R^2$|⁠.