中文摘要：

大幅度、快速光变是BLLac天体的重要特征之一,光变研究对探索BLLac天体内部的物理过程和机理具有特殊的意义.从大量文献中收集了BLLac天体S50716＋714光学V,R,I3个波段从1994年到2008年的有效观测数据,并将这些数据30天平均后进行自回归模型（AR）的双谱估计.双谱的等高线图和对角切片图表明,双谱估计能消除噪声的干扰来提取有用信息,抑制了噪声、提高了信噪比,有很高的分辨率,避免了伪峰的出现,能准确地认证BLLac天体的光变周期值.由V,R,I3个波段的双谱等高线图和对角切片图发现BLLac天体S50716＋714具有3.33年和3.47年的光变周期,这个结论和Raiteri等发现的3.3年周期是一致的,其在2007年爆发了一次,预测下次将在2011—2012年爆发。

英文摘要：

Large and rapid variability is one of the defining properties of BL Lac objects.Variability in BL Lac objects has always served as a powerful and important tool for inquring into the physics of these unusual objects.From an extensive seach in the literature we have collected a total of data points of effective observations of BL Lac object S5 0716 ＋ 714 in V,R and I bands from 1994 to 2008.Then these data are processed on 30 days baseline by autoregressive bispectrum model.In order to eliminate noise interference to extract useful information in the background of Gaussian noise,we propose a method of signal analysis and processing,which analyzes the additive Gaussion noise signal based on autoregressive bispectrum model.Bispectrum is not sensitive to Gaussian noise,it not only suppresses the Gaussion noise in the signal and greatly improves the signal to noise ratio,but also can identify the periodical variations of BL Lac objects.Our results show that the long term periods of variation are 3.33 years and 3.47 years.The conclusion is consistent with 3.3 years period which was found by Raiteri et al.The brightness peak was observed in 2007,so we expect the next burst in 2011—2012.