Variability Periodicity Analysis of 3C 273 Based on EMD-AR Spectrum

Abstract

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 a 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, and 2.76 yr, which were in good agreement with that reported in the literature. The short time scale periods were (30$\pm$1), (15$\pm$ 0.3), (7.5 $\pm$ 0.2), (10 $\pm$ 0.1), (5 $\pm$ 0.6) and (6 $\pm$ 0.4), and (3 $\pm$ 0.5) min. There is an approximate period-doubling relationship among these possible periods, which has not been reported before, and may provide reference for further research.