Simulation of the X-ray light curves of intermediate polars

Norton, A. J. (1993). Simulation of the X-ray light curves of intermediate polars. Monthly Notices of the Royal Astronomical Society, 265(2) pp. 316–328.



A technique is presented for simulation of the X-ray light curves of intermediate polars. The model includes the effects of self-occultation of the emission regions by the body of the white dwarf, and variation of photoelectric absorption and electron scattering as the aspect angles of the emission regions change, and the effect of accretion occurring through a disc, directly via the accretion stream or by a combination of both. Both the variation of the rate of accretion on to a given emission region and its effective `migration' around the magnetic pole are taken into account. These features naturally arise in a system that is fed (at least in part) directly by the stream. Results are considered for two specific emission-region geometries, namely a filled circle and a semicircular arc, over a wide range of parameter space in each case. Disc-fed, non-accretion disc and discless accretion are each considered, both in the low and high X-ray energy regime and at a range of inclination angles and magnetic axis offset angles. The main conclusion of this work is that very complex pulse profiles can result from innately symmetrical geometrical and physical situations. The results obtained in the case of discless accretion feeding arc-shaped emission regions are compared with recent observational data and shown to produce qualitatively similar profiles. Finally, ways are considered in which this simple approach may be extended to include a more realistic description of the conditions that exist in intermediate polars.

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