A Study on the Light-Curve Periodicity of the Cyg X-1 Based on the Jurkevich Method

The Jurkevich method is an effective method to search for periodicities in an observational time-sequence data set. Unlike most existing methods, the present one is based on an analysis of variances and does not require data to be evenly sampled in time. Therefore, the method can reflect real periodicities of the data. In this paper, we first give an account of the Jurkevich method and the Kidger Criteria. We then use these to analyze All-Sky Monitor (1.5-12keV) data of the Rossi X-Ray Timing Explorer (RXTE) during January 1996 to October 2011. From the result, we find that the light curve of the black-hole candidate X-ray binary Cyg X-1 exhibits 363±11.5 day and 51±1.4 day periodicities. We present the results of Benlloch et al (2004) during December 1996 to July 2001, which are based on the Power Spectrum Density (PSD) method. We find from their data that the Cyg X-1 light curve has the 150 day and 420 day periodicities. We also compare the results of the PSD method to those of the Jurkevich method, and come to the conclusion that (1) the 363±11.5 day period is likely real, (2) the 51±1.4 day period is likely real, (3) but the 150 day period may be only an artifact caused by the 51±1.4 day periodicity.