The Anisotropic Transfer of Resonance Photons in Hot Plasmas on Magnetized White Dwarfs

Abstract

In order to confirm the anisotropic effect of resonance photons in hot accretion columns on white dwarfs in magnetic cataclysmic variables, proposed by Terada etal (2001), systematic studies with ASCA of 7 polars and 12 intermediate polars are performed. The equivalent widths of He-like Fe K$_α$ line of polars are found to be systematically modulated at their spin periods in such a way that it increases at the pole-on phase. This implies that the anisotropic mechanism is commonly operating among polars. On the other hand, those of intermediate polars are statistically consistent with being unmodulated with an upper limit of 1.5 times modulation. This may be due to a different accretion manner like aurora curtain (Rosen etal 1988) so that the plasma becomes optically thin along the horizontal axis also for the resonance lines, or because of larger optical depths for Compton scattering if the emission regions have the same coin-like shapes as polars.