Iron Kα lines and the absorption structure of intermediate polars

Abstract

The X-ray spectra of Intermediate Polars typically show a large absorbing column density and a strong iron Kα emission line. Using observations made with EXOSAT and GINGA, we show that the lines probably have a fluorescent origin but that their equivalent widths are too large to be due to fluorescence solely in the material which gives rise to the measured column density, assuming a single value for NH in the vicinity of the emission region. To explain this we suggest that the spectra are absorbed by a continuous distribution of column densities. We show that a power law form for this distribution gives rise to line equivalent widths of several hundred eV, as observed, and also provides acceptable fits to the X-ray continua. We further suggest that a distribution of column densities would arise naturally as a result of the “blob-model” for accretion in magnetic Cataclysmic Variables.