Compton Scattering of Fe Kα Lines from Accreting White Dwarfs

Abstract

Compton scattering in the bulk accretion flow of the accretion column in magnetic cataclysmic variables can significantly shift photon energies in the X-ray emission lines resulting from accretion shocks. In particular, Compton recoil can potentially broaden the 6.7 and 6.97 keV Fe Kα emission lines produced in the post-shock region, and contaminate the fluorescent 6.4 keV neutral Fe Kα line reflected off the white dwarf surface. We present nonlinear Monte Carlo simulations demonstrating these effects, and we discuss the interpretation of observed Fe Kα linewidths in magnetic cataclysmic variables in light of these new results. The implications for other accreting compact objects are also discussed.