基于EMD-AR谱的3C 273光变周期分析

Variability Periodicity Analysis of 3C 273 Based on EMD-ARSpectrum

光变是Blazar最显著的观测特征之一,有的光变呈准周期性.Blazar周期光变可能为其中心黑洞和吸积盘等内部物理结构提供重要信息.因此,周期分析对于讨论Blazar的光变有重要意义.结合经验模态分解(Empirical Mode Decomposition,EMD)和自回归(Auto-regressive,AR)模型谱估计方法的优点,提出了一种基于EMD-AR谱的组合光变周期分析新方法.先对观测数据进行EMD分解,得到各阶模态分量,并计算其与原始光变曲线的相关系数,再取相关度高的分量求和后估算AR谱,最后将此功率谱的周期分析方法用于天体的光变数据分析.讨论了EMD-AR谱方法的原理和应用步骤,并用此方法对类星体3C 273在1887—2016年的观测数据进行了分析,得到3C 273的长时标周期分别为:21.23、13.51、11.02、5.51、4.69、3.79、2.76 yr,与文献中常用方法的分析结果有很好的一致性;短时标周期分别为:(30±1)、(15±0.3)、(7.5±0.2)、(10±0.1)、(5±0.6)、(6±0.4)和(3±0.5)min,此结果未见相关报道,这些可能的周期相互还存在近似倍周期的关系,可为进一步的研究提供参考.

Light variation is one of the most significant observation features of Blazar,some of which are quasi periodic.The analysis of Blazar’s variability periodicity can provide important information for explaining the internal physical structure of its central black hole and accretion disk.In this paper,benefited from the advantages of empirical mode decomposition(EMD)and auto-regressive(AR)model spectrum estimation methods,a combined variability periodicity analysis method is proposed based on the EMD-AR spectrum.First,EMD is used to decompose the observed data to obtain the modal components,and the correlation coefficient between them and the original light variation curve are calculated.Then,the variability periodicity of the components with high correlation is estimated and summed.Finally,the light variation period of Blazar is calculated by using the power spectrum.The principle and application steps of EMD-AR spectrum method are discussed,and the observational data of quasar 3C 273 from 1887 to 2016 are analyzed with this method.The long time scale periods of object 3C 273 were 21.23,13.51,11.02,5.51,4.69,3.79,2.76 years,which were in good agreement with that reported in the literature.The short time scale periods were(30±1),(15±0.3),(7.5±0.2),(10±0.1),(5±0.6)and(6±0.4),(3±0.5)minutes.There is an approximate period-doubling relationship among these possible periods,which has not been reported before and may provide reference for further research.