X-ray beaming caused by resonance scattering in the accretion column of magnetic cataclysmic variables

Extremely strong ionized Fe emission lines, with equivalent widths reaching similar to 4000 eV, were discovered by ASCA from a few Galactic compact ob jects, including AX J2315-0592, RX J1802.1 + 1804 and AX J1842.8-0423. Thes e objects are thought to be binary systems containing magnetized white dwar fs (WDs). A possible interpretation of the strong Fe K line is the line-pho ton collimation in the WD accretion column, as a result of resonance scatte ring of line photons. The collimation occurs when the accretion column has a flat shape, and the effect is augmented by the vertical velocity gradient , which reduces the resonant trapping of resonant photons along the magneti c field lines. This effect was quantitatively confirmed with Monte Carlo si mulations. Furthermore, with ASCA observations of the polar V834 Centauri, this collimation effect was clearly detected as a rotational modulation of the equivalent width of the Fe K emission line. The extremely strong emissi on lines mentioned above can be explained consistently by our interpretatio n. Combining this effect with other X-ray information, the geometry and pla sma parameters in the accretion column were determined.