The changing X-ray light curves of the intermediate polar FO Aquarii
The changing X-ray light curves of the intermediate polar FO Aquarii
复制标题
中间极性 FO Aquarii 变化的 X 射线光变曲线
DOI：
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发表时间：
1998
期刊：
影响因子：
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通讯作者：
C. Hellier
中科院分区：
文献类型：
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作者：
A. Beardmore;K. Mukai;A. Norton;J. Osborne;C. Hellier
Comparison of five X-ray observations of the intermediate polar FO Aqr reveals that the morphology of the X-ray light curve changes considerably with time. In particular, power spectra of the 1988 Ginga and 1993 ASCA data reveal strong sideband and orbital variations, whereas the 1990 Ginga observation does not. This suggests that the amount of stream-fed accretion varies with epoch, and the system was accreting predominantly from a disc in 1990. In contrast to other intermediate polars, the X-ray spin-pulse profiles show significant variations between observations, ranging from relatively sinusoidal to sawtooth-shaped at medium energies. During the 1988 and 1990 observations a notch is visible at spin phase zero, due to the presence of an interpulse at phase 0.85, which is absent during the other observations. At lower energies a narrow pulse of emission is seen at spin phase 0.2. We interpret the pulse profile from the 1990 Ginga observation using a model for accretion from a disc on to a dipolar magnetic field, the axis of which is offset from the white dwarf centre by ~ 0.15 white dwarf radii. In order to account for the later occurrence of the hardness-ratio maximum in 1988 and 1993, we suggest that the accretion-rate profile changes so that accretion is favoured along the field lines which trail the magnetic pole. This also accounts for the disappearance of the interpulse and notch in 1993.
