Characterizing Long-term Optical Variability Properties of γ-Ray-bright Blazars

Optical observations of a sample of 12 gamma-ray-bright blazars from four optical data archives-American Association of Variable Star Observers, Small and Moderate Aperture Research Telescope System, Catalina, and Steward Observatory-are compiled to create densely sampled light curves spanning more than a decade. As a part of the blazar multiwavelength studies, several methods of analysis, e.g., flux distribution and rms-flux relation, are performed on the observations with the aim to compare the results with the similar ones in the gamma-ray band presented in Bhatta & Dhital. It is found that, similar to the gamma-ray band, blazars display significant variability in the optical band that can be characterized with lognormal flux distribution and a power-law dependence of rms on flux. It could be an indication of a possible inherent linear rms-flux relation, yet the scatter in the data does not allow to rule out other possibilities. When comparing variability properties in the two bands, the blazars in the gamma-rays are found to exhibit stronger variability with a steeper possible linear rms-flux relation and a flux distribution that is more skewed toward higher fluxes. The cross-correlation study shows that except for source 3C 273, the overall optical and the gamma-ray emission in the sources are highly correlated, suggesting a cospatial existence of the particles responsible for both the optical and gamma-ray emission. Moreover, sources S5 0716+714, Mrk 421, Mrk 501, PKS 1424-418, and PKS 2155-304 revealed possible evidence of quasiperiodic oscillations in the optical emission with the characteristic timescales, which are comparable to those in the gamma-ray band detected in our previous work.