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arXiv 0907.3515astro-ph.HE
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亮银河系X射线双星的状态跃迁:亮度跨越两个数量级

State Transitions in Bright Galactic X-ray Binaries: Luminosities Span by Two Orders of Magnitude

Wenfei Yu, Zhen Yan

摘要:

利用RXTE上的ASM和Swift上的BAT的X射线监测观测,我们能够研究大约20个明亮的持久和瞬态黑洞和中子星双星的光谱态跃迁。我们证实了硬态到软态跃迁对应的X射线亮度与随后软态的X射线亮度之间存在相关性。这种相关性在两个数量级的光度范围内保持不变,没有通量饱和或截止的迹象。我们还发现,在爆发或耀斑的上升阶段,跃迁光度与X射线光度的增加率相关,这意味着跃迁光度变化的起源与瞬态源和持久源的非定常吸积有关。软到硬的过渡和前面的软态的峰值亮度的结束对应的亮度之间的相关性被发现是微不足道的。结果表明,当质量吸积率增大时,谱态跃迁的滞后效应主要是由非定常吸积驱动的.我们的研究结果还表明,银河系X射线双星可以达到更明亮的硬态爆发期间,更高的光度和类似的上升时间尺度的观察。根据这些关联,我们推测下个世纪在银河系双星中将观测到超过爱丁顿光度的明亮硬态。我们还认为,在附近星系中的一些超亮X射线源,在明亮的短耀斑期间停留在硬态,窝藏恒星质量的致密星。

英文摘要:

Using X-ray monitoring observations with the ASM on board the RXTE and the BAT on board the Swift, we are able to study the spectral state transitions occurred in about 20 bright persistent and transient black hole and neutron star binaries. We have confirmed that there is a correlation between the X-ray luminosity corresponding to the hard-to-soft transition and the X-ray luminosity of the following soft state. This correlation holds over a luminosity range spanning by two orders of magnitude, with no indication of a flux saturation or cut-off. We have also found that the transition luminosity correlates with the rate of increase in the X-ray luminosity during the rising phase of an outburst or flare, implying that the origin of the variation of the transition luminosity is associated with non-stationary accretion in both transient sources and persistent sources. The correlation between the luminosity corresponding to the end of the soft-to-hard transition and the peak luminosity of the preceding soft state is found insignificant. The results suggest that the hysteresis effect of spectral state transitions is primarily driven by non-stationary accretion when the mass accretion rate increases rather than the mass accretion rate decreases. Our results also imply that Galactic X-ray binaries can reach more luminous hard states during outbursts of higher luminosities and of similar rise time scales as those observed. Based on the correlations, we speculate that bright hard state beyond the Eddington luminosity will be observed in Galactic binaries in the next century. We also suggest that some ultra-luminous X-ray sources in nearby galaxies, which stay in the hard states during bright, short flares, harbor stellar-mass compact stars.

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