硬X射线共生星RT Cru的性质
The Nature of the Hard-X-Ray Emitting Symbiotic Star RT Cru
摘要：
我们描述钱德拉高能量透射光栅光谱仪观测RT Cru，第一个新的子类的共生星，似乎包含白矮星（WD）能够产生硬X射线发射大于50千电子伏。这种硬X射线发射的产生在这个子类中的对象（其中还包括CD-57 3057，T CrB和CH Cyg）挑战了我们对吸积WD的理解。我们发现，0.3 - 8.0 keV的X射线光谱的RT克鲁发出的等压冷却流，在光学薄吸积盘边界层的一些矮新星。光谱拟合的参数证实了致密吸积体是WD，它们与WD是大质量的一致。我们检测到快速，随机的变化，从X射线发射低于4千电子伏。闪烁的变化和冷却流光谱的组合表明RT Cru很可能是通过盘吸积提供动力的。而最硬的X射线发射的激变变星是典型的磁吸积物，X射线通量调制在WD自旋周期，我们发现，从RT Cru的X射线发射不是脉冲。因此，RT克鲁没有证据表明磁通道吸积，符合我们的解释，钱德拉光谱来自吸积盘边界层。
英文摘要：
We describe Chandra High-Energy Transmission Grating Spectrometer observations of RT Cru, the first of a new sub-class of symbiotic stars that appear to contain white dwarfs (WDs) capable of producing hard X-ray emission out to greater than 50 keV. The production of such hard X-ray emission from the objects in this sub-class (which also includes CD -57 3057, T CrB, and CH Cyg) challenges our understanding of accreting WDs. We find that the 0.3 -- 8.0 keV X-ray spectrum of RT Cru emanates from an isobaric cooling flow, as in the optically thin accretion-disk boundary layers of some dwarf novae. The parameters of the spectral fit confirm that the compact accretor is a WD, and they are consistent with the WD being massive. We detect rapid, stochastic variability from the X-ray emission below 4 keV. The combination of flickering variability and a cooling-flow spectrum indicates that RT Cru is likely powered by accretion through a disk. Whereas the cataclysmic variable stars with the hardest X-ray emission are typically magnetic accretors with X-ray flux modulated at the WD spin period, we find that the X-ray emission from RT Cru is not pulsed. RT Cru therefore shows no evidence for magnetically channeled accretion, consistent with our interpretation that the Chandra spectrum arises from an accretion-disk boundary layer.
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