2006PASJ...58..797F

We reported the result of the long-term optical variability of the blazar 4C 29.45s (QSO 1156+295, Ton 599), carried out by optical photometric observations in the Johnson V, Cousins RI passbands during 1997 April to 2002 March. We used the 1.56-m telescope of the Shanghai Astronomical Observatory at Sheshan, China, and compiled the post-1974 optical photometric data of the blazar by combining our new observations with the published optical data, and found maximum variations in different passbands: DU = 4.41mag, DB = 5.55mag, DV = 4.53mag, DR = 5.80mag, and DI = 5.34mag. The average color indices are: U - B = -0.54 ± 0.18mag, B - V = 0.56 ± 0.21mag, B - R = 0.93 ± 0.18mag, B - I = 1.51 ± 0.24mag, V - R = 0.44 ± 0.15mag, and V - I = 1.03 ± 0.23mag. The post-1974 data give us an excellent opportunity to search for the existence of a possible periodicity in the light curve. In searching for periodicity in the R passband light curve, we performed a Jurkevich test and power spectral (Fourier) analysis methods, as well as CLEANest algorithms to remove false signals. We found possible periods of 3.55 and 1.58 years. A possible mechanism for the periodic variability was analyzed.