Long term variability of Cygnus X-1. I. X-ray spectral-temporal correlations in the hard state
Long term variability of Cygnus X-1. I. X-ray spectral-temporal correlations in the hard state
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DOI：
10.1051/0004-6361:20030906
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发表时间：
2002-02
影响因子：
6.5
通讯作者：
K. Pottschmidt;J. Wilms;M. Nowak;G. Pooley;T. Gleißner;W. Heindl;D. Smith;R. Remillard;R. S. I. Tuebingen;Mit;M. Cambridge;Cass;Ucsd;Ssl;Ucb
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作者：
K. Pottschmidt;J. Wilms;M. Nowak;G. Pooley;T. Gleißner;W. Heindl;D. Smith;R. Remillard;R. S. I. Tuebingen;Mit;M. Cambridge;Cass;Ucsd;Ssl;Ucb
我们展示了1998年至2001年使用罗西X射线计时探测器（RXTE）监测的0.002-128 Hz频率范围内黑洞候选者天鹅座X-1计时特性的长期演变。在此期间的大部分时间里，震源处于坚硬状态。功率谱密度（PSD）是很好的建模为四个洛伦兹，这描述了不同的宽噪声分量的总和。在1998年7月之前，天鹅座X-1处于一种“安静”的硬态，主要特征是前三个大洛伦兹星系占主导地位。在1998年5月前后，这种行为发生了变化：总的分数均方根振幅下降，洛伦兹峰的峰值频率增加，平均时间滞后略有增加，X射线谱变软。定时参数的变化主要是由于第三洛伦兹算子的幅度的强烈减小。自这一事件以来，已经观察到异常大量的X射线耀斑，我们将其归类为“失败的状态转换”。在这些失败的状态转换期间，X射线功率谱改变为中间状态的功率谱。用四个Lorentzian对PSD进行建模，我们发现在状态转换过程中，第一个Lorentzian分量相对于第二个和第三个Lorentzian分量被抑制。我们还证实了我们以前的结论，即在这些过渡期间，在3.2-10 Hz频带内，频率相关的时间滞后显著增加。我们确认的解释耀斑失败的状态转换与观察2001年1月和2001年10月的软状态。PSD和X射线滞后的行为表明，一些或所有的洛伦兹分量与负责硬态谱的吸积盘日冕。我们讨论我们的结果的物理解释。
We present the long term evolution of the timing properties of the black hole candidate Cygnus X-1 in the 0.002-128 Hz frequency range as monitored from 1998 to 2001 with the Rossi X-ray Timing Explorer (RXTE). For most of this period the source was in its hard state. The power spectral density (PSD) is well modeled as the sum of four Lorentzians, which describe distinct broad noise components. Before 1998 July, Cyg X-1 was in a "quiet" hard state characterized primarily by the first three of these broad Lorentzians being dominant. Around 1998 May, this behavior changed: the total fractional rms amplitude decreased, the peak frequencies of the Lorentzians increased, the average time lag slightly increased, and the X-ray spectrum softened. The change in the timing parameters is mainly due to a strong decrease in the amplitude of the third Lorentzian. Since this event, an unusually large number of X-ray flares have been observed, which we classify as "failed state transitions". During these failed state transitions, the X-ray power spectrum changes to that of the intermediate state. Modeling this PSD with the four Lorentzians, we find that the first Lorentzian component is suppressed relative to the second and third Lorentzian during the state transitions. We also confirm our previous conclusion that the frequency-dependent time lags in- crease significantly in the 3.2-10 Hz band during these transitions. We confirm the interpretation of the flares as failed state transitions with observations from the 2001 January and 2001 October soft states. Both the behavior of the PSD and the X-ray lag suggest that some or all of the Lorentzian components are associated with the accretion disk corona responsible for the hard state spectrum. We discuss the physical interpretation of our results.