X-ray beaming caused by resonance scattering in the accretion column of magnetic cataclysmic variables |
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| Authors: | Y Terada M Ishida K Makishima T Imanari R Fujimoto K Matsuzaki H Kaneda |
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| Institution: | 1Department of Physics and Science, University of Tokyo, 7-3-1, Hongo, Bunkyo-lu, Tokyo, 113-0033 Japan;2Department of Physics, Tokyo Metropolitan University, 1-1 Minami-Ohsawa, Hachioji-shi, Tokyo, 192-0397 Japan 3Engineering, The University of Tokyo, 7-3-1, Hongo, Bunkyo-lu, Tokyo, 113-0033 Japan 4 The Institute of Space and Astronautical Science, 3-1-1, Yoshinodai, Sagamihara, 229-8510 Japan |
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| Abstract: | Extremely strong ionized Fe emission lines, with equivalent widths reaching ～4000 eV, were discovered by ASCA from a few Galactic compact objects, including AX J2315?0592, RX J1802.1+1804 and AX J1842.8?0423. These objects are thought to be binary systems containing magnetized white dwarfs (WDs). A possible interpretation of the strong Fe K line is the line-photon collimation in the WD accretion column, as a result of resonance scattering 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 magnetic field lines. This effect was quantitatively confirmed with Monte Carlo simulations. 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 emission lines mentioned above can be explained consistently by our interpretation. Combining this effect with other X-ray information, the geometry and plasma parameters in the accretion column were determined. |
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| Keywords: | radiation mechanisms: thermal scattering methods: observational stars: individual: V834 Cen white dwarfs X-rays: stars |
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