In this work, four methods are introduced to analyse the unevenly sampled data. The four methods are power spectral density, autocorrelation function, structure function and Jurkevich method. Some interesting mathematical links are derived amongst the four methods. These links show that the four methods have the same performance. For the Jurkevich method, the effect of the width of bins is apparent. If the width is half the time scale, the method has better performance.

OJ 287 is a BL Lac object at redshift 𝑧 = 0.306 that has shown double-peaked bursts at regular intervals of 12 yr during the last 40 yr according to previous research. Some of the AGN 𝛾 ray power density shows a white noise process, while some others shows a red noise process. Some AGN flux presents normal or log-normal distribution. The two processes have an intrinsic relationship with centre black hole emission mechanism. We present the results of the analysis of the Fermi-LAT data. We review some problems concerning the random process.