Study On Quasi-Periodic Oscillations Of Blazars Variability

Blazars are an important subclass of radio-loud active galactic nuclei(AGNs)with non-thermal continuum emission ranging from radio to high-energy Gamma-rays,rapid and violent variability across the entire electromagnetic spectrum,and high and variable polarization at radio and optical energies.Any quasi-periodic variations discovered in blazar light curves would contain important information on the location and nature of the processes within the emission regions.In non-blazar active galactic nuclei,particularly Seyfert galaxies,any such fluctuations are very likely to be associated with the accretion disks,but in blazars they would almost certainly have to emanate from jetsIn this paper,we discuss the different methods for finding quasi-periodic oscilla-tions(QPO)and research for the quasi-periodic oscillations in long-term variability of the blazars.We analyze the QPO on gamma-ray and optical band light curve of BL Lac S2 0109 + 22 with two different and suitable methods.we obtained S20109 + 22 evenly sampled gamma-ray light curve lasted about 10 years,and we access unevenly sampled light curve lasted about 8 years in the optical band.We use the wavelet analysis method and the Lomb-Scargle periodogram(LSP)method to study the possible quasi-periodic variabilities of the light curves.For the evenly sampled light curve in the gamma-ray band,we have found the periodicity signal about 925.61 days with wavelet analysis method,giving a significance of?2 ?(95%).Alternatively,we find an about?1000 days signal using LSP method with the significance of about 3?.The result indicates that there is no QPO signal found in this analysis.In addition,we use the LSP method to analyze S2 0109 + 22 unevenly sampled light curve in the optical band and we have found the periodic-ity signal about 401.9 days with the significance of?5 ?(99.947%).In this case,we probably have found a rough QPO signal for this object.For the divergency between the optical and gamma-ray band,we suggest that it might be caused by that the emission region of optical and gamma-ray band is not the same.Moreover,further long-term multi-wavelength monitoring of this blazar is needed to confirm its quasi-periodicity.