Optical and radio variability in blazars
Аннотация
We have analyzed the optical (0.44 micron) and radio flux density variations (4.8,8.0, and 14.5 GHz) of the five best observed variable active galactic nuclei, of which three are BL Lacertae (BL Lac) objects and two are optically violent variable (OVV) quasars: 2200+420 (BL Lac), 0851+202 (OJ 287), 1641+399 (3C 345), 0735 + 178, and 2223-052 (3C 446). For each object, the nature of the variability at individual wavelengths is determined by using a structure function analysis and the autocorrelation function as calculated from the discrete correlation technique. Both techniques yield similar results, showing that the optical variations are similar for all objects and are a combination of flicker and shot noise. The radio variability is distinct, being described by shot noise (less variation at short times), with the two OVVs showing the most extreme behavior. The time lag between the variations at the three radio frequencies and the optical flux is studied with the discrete cross-correlation function and the mean variance methods. The three radio frequencies are well correlated, with a time delay of months for the lower luminosity objects and longer for the higher luminosity sources. The optical and radio data are weakly correlated, with a time delay of ~1 yr for all five sources. Taken together, these results indicate that the optical and radio emitting regions are physically related, exist on distinct size scales, and excite their synchrotron emitting plasmas differently. The greatest difficulty in performing this analysis is the inadequate sampling of the optical emission, and an improved strategy for data acquisition is recommended.