天鹅座X-1的可变超轨道调制
The variable super-orbital modulation of Cygnus X-1
摘要：
我们研究了天鹅座X-1的X射线数据中存在的超轨道调制，通常归因于吸积盘和相对论喷流的进动。在Swift/BAT和RXTE/ASM光变曲线（LC）中，我们发现了一个新的、强的、从2005年开始的326+-2 d周期调制。我们还调查了Vela 5 B/ASM和ArielV/ASM的档案数据，证实了以前报道的~290 d周期调制，因此证实了超轨道周期不是恒定的。最后，我们研究RXTE/ASM LC在2005年之前，发现以前报道的~150 d周期是最有可能的工件，由于使用基于傅立叶功率的分析假设下，调制具有恒定的周期沿整个数据样本。相反，我们发现强烈的迹象表明，几个离散的变化的岁差周期，发生在巧合的软和失败的状态转换插曲。我们还发现了调制的周期和幅度之间的相关性。2006年9月，MAGIC探测到100 GeV以上的伽马射线，这与超轨道调制的最大值相吻合。下一个最大值将发生在2008年7月2日至14日之间，当时天鹅座X-1的地面切伦科夫望远镜（如MAGIC和VERITAS）的观测条件是最佳的。
英文摘要：
We study the super-orbital modulation present in the Cygnus X-1 X-ray data, usually attributed to the precession of the accretion disk and relativistic jets. We find a new, strong, 326+-2 d period modulation starting in 2005, in Swift/BAT and RXTE/ASM light curves (LCs). We also investigate Vela5B/ASM and ArielV/ASM archival data and confirm the previously reported ~290 d periodic modulation, and therefore confirming that the super-orbital period is not constant. Finally, we study RXTE/ASM LC before 2005 and find that the previously reported ~150 d period is most likely an artifact due to the use of a Fourier-power based analysis under the assumption that the modulation has a constant period along the whole data sample. Instead, we find strong indications of several discrete changes of the precession period, happening in coincidence with soft and failed state-transition episodes. We also find a hint of correlation between the period and the amplitude of the modulation. The detection of gamma-rays above 100 GeV with MAGIC in September 2006 happened in coincidence with a maximum of the super-orbital modulation. The next maximum will happen between 2 and 14 of July 2008, when the observational conditions of Cygnus X-1 with ground-based Cherenkov telescopes, such as MAGIC and VERITAS, are optimal.
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