Hard X-Ray Flares Preceding Soft X-Ray Outbursts in Aquila X-1: A Link between Neutron Star and Black Hole State Transitions
Hard X-Ray Flares Preceding Soft X-Ray Outbursts in Aquila X-1: A Link between Neutron Star and Black Hole State Transitions
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DOI：
10.1086/375714
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发表时间：
2003-04
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影响因子：
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通讯作者：
Wenfei Yu;M. Klein-Wolt;R. Fender;M. van der Klis
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作者：
Wenfei Yu;M. Klein-Wolt;R. Fender;M. van der Klis
分析了1999年5月/6月和2000年9月/10月天鹰座X-1中子星星瞬变爆发期间的Rossi X射线计时探测器数据。我们发现，在这些爆发的早期上升，在15 keV以上的能量范围内的硬耀斑之前的软X射线峰。硬耀斑的硬X射线通量在最大值时比爆发中的任何其他点都强3倍以上。硬X射线耀斑上升到这个最大值与单调增亮的低/硬态光谱是一致的。在硬耀斑的峰值之后，在8-12 keV的范围内发生了急剧的光谱跃迁。定时分析表明，在硬耀斑期间，功率谱主要由带限噪声和1-20 Hz准周期振荡（QPO）组成，它们在频率上是相关的。在硬耀斑之后，功率谱立即变成幂律噪声。在硬耀斑期间和之后的光谱和定时特性非常类似于在爆发的早期上升期间的黑洞瞬变。我们认为，这些硬耀斑和光谱跃迁在Aql X-1是相同的起源，在黑洞瞬变观测。这导致Aql X-1中的1-20 Hz QPO和带限噪声与黑洞瞬变中的QPO和带限噪声相关联。我们讨论了这一发现对我们理解软X射线瞬态爆发，状态转换和X射线双星的变化的影响。
We have analyzed Rossi X-Ray Timing Explorer data of the neutron star transient Aquila X-1 obtained during its outbursts in 1999 May/June and 2000 September/October. We find that in the early rise of these outbursts, a hard flare in the energy range above 15 keV preceded the soft X-ray peak. The hard X-ray flux of the hard flares at maximum was more than a factor of 3 stronger than at any other point in the outbursts. The rise of the hard X-ray flare to this maximum was consistent with a monotonically brightening low-/hard-state spectrum. After the peak of the hard flare, a sharp spectral transition occurred with spectral pivoting in the range 8-12 keV. Our timing analysis shows that during the hard flare, the power spectra were composed mainly of band-limited noise and a ~1-20 Hz quasi-periodic oscillation (QPO), which correlate in frequency. Immediately after the hard flare, the power spectra turned into power-law noise. The spectral and timing properties during and after the hard flares are very similar to those in black hole transients during the early rise of an outburst. We suggest that these hard flares and spectral transitions in Aql X-1 are of the same origin as those observed in black hole transients. This leads to the association of the 1-20 Hz QPOs and band-limited noise in Aql X-1 with those in black hole transients. We discuss the impact of this discovery on our understanding of soft X-ray transient outbursts, state transitions, and variability in X-ray binaries.