仙后座γ中快速运动部分X射线吸收体的发现
Discovery of Rapidly Moving Partial X-ray Absorbers within gamma Cassiopeiae
摘要：
仙后座γ是一颗神秘的Be星，具有异常强烈的硬X射线发射。朱雀天文台在2011年的一次持续时间约为100千秒的观测中发现了6次快速X射线光谱硬化事件，称为“软度下降”。所有的软度下降事件都显示出对称的软度比变化，其中一些事件的底部明显是由于饱和而平坦的。软度凹陷光谱最好用~40%或~70%的部分覆盖吸收来描述，所述部分覆盖吸收由具有~2- 8 e21 cm-2的中性氢柱密度的物质对kT ~12 keV等离子体发射，而这些凹陷之外的光谱几乎没有吸收。这一结果表明，在伽马Cas系统中存在两个不同的X射线发射点，可能是在一个具有偶极质量吸积的白矮星伴星上。部分覆盖的吸收体可能是Be星风中的斑点，Be盘，或围绕白矮星伴星旋转。软比的硬X射线通量的弱相关性表明，在kT ~0.9和5 keV的稳定等离子体的存在下，这可能是来自Be或白矮星风。Be星和白矮星双星系统的形成需要在两颗恒星之间进行质量转移; Cas γ可能在过去经历过这样的活动。
英文摘要：
Gamma Cassiopeiae is an enigmatic Be star with unusually strong hard X-ray emission. The Suzaku observatory detected six rapid X-ray spectral hardening events called "softness dips" in a ~100 ksec duration observation in 2011. All the softness dip events show symmetric softness ratio variations, and some of them have flat bottoms apparently due to saturation. The softness dip spectra are best described by either ~40% or ~70% partial covering absorption to kT ~12 keV plasma emission by matter with a neutral hydrogen column density of ~2-8e21 cm-2, while the spectrum outside of these dips is almost free of absorption. This result suggests the presence of two distinct X-ray emitting spots in the gamma Cas system, perhaps on a white dwarf companion with dipole mass accretion. The partial covering absorbers may be blobs in the Be stellar wind, the Be disk, or rotating around the white dwarf companion. Weak correlations of the softness ratios to the hard X-ray flux suggest the presence of stable plasmas at kT ~0.9 and 5 keV, which may originate from the Be or white dwarf winds. The formation of a Be star and white dwarf binary system requires mass transfer between two stars; gamma Cas may have experienced such activity in the past.
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