An Analysis of the Light Variations of 3C 345 and 3C 273

By means of the structural function analysis, we have studied the variability of the classical blazars 3C273 and 3C345 at 22 GHz & 37 GHz and in an optical waveband. Our results show that the periodicity of 3C273 is rather evident: at 22 GHz, the periods of 7.0 and 14.7 years exist; at 37 GHz, the periods of 7.2 and 14.5 years exist; and in the optical waveband, the periods of 0.7 and 8.7 years probably exist. 3C345 has a rather evident period of 8.8 years at 37 GHz, and the not very evident periods of 9.3 and 10.2 years at 22 GHz and in the optical waveband, respectively.