类星体时域巡天中的假周期
False periodicities in quasar time-domain surveys
摘要：
最近有几个报告表明类星体的光变曲线存在明显的周期性变化，例如Graham等人的PG 1302-102（2015 a）。任何显示出亮度周期性振荡的类星体都将是一个强有力的候选者，成为一个紧密的双超大质量黑洞，反过来，也是引力波研究的候选者。然而，正常的类星体--由吸积到单个超大质量黑洞上提供动力--通常在很大的时间尺度上表现出随机变化。因此，重要的是要仔细评估的方法，以确定周期性的候选人从人口占主导地位的随机变异。使用贝叶斯分析的PG 1302-102的光变曲线，我们发现，一个简单的随机过程是首选的正弦变化。然后，我们讨论了一些问题时遇到的搜索罕见的，严格的周期性信号之间的大量不规则采样，随机时间序列，并使用模拟类星体的光变曲线来说明这些点。从几千个陡峭的频谱（“红噪声”）随机过程的模拟，我们发现许多模拟，显示几个周期的周期性，如PG 1302-102中看到的。我们强调的重要性，校准的假阳性率时，在搜索中的目标的数量是非常大的。
英文摘要：
There have recently been several reports of apparently periodic variations in the light curves of quasars, e.g. PG 1302-102 by Graham et al. (2015a). Any quasar showing periodic oscillations in brightness would be a strong candidate to be a close binary supermassive black hole and, in turn, a candidate for gravitational wave studies. However, normal quasars -- powered by accretion onto a single, supermassive black hole -- usually show stochastic variability over a wide range of timescales. It is therefore important to carefully assess the methods for identifying periodic candidates from among a population dominated by stochastic variability. Using a Bayesian analysis of the light curve of PG 1302-102, we find that a simple stochastic process is preferred over a sinusoidal variations. We then discuss some of the problems one encounters when searching for rare, strictly periodic signals among a large number of irregularly sampled, stochastic time series, and use simulations of quasar light curves to illustrate these points. From a few thousand simulations of steep spectrum (`red noise') stochastic processes, we find many simulations that display few-cycle periodicity like that seen in PG 1302-102. We emphasise the importance of calibrating the false positive rate when the number of targets in a search is very large.
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