Optical Photometrical Observations and Variability for Quasar 4C 29.45

Abstract 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: $\Delta U = 4.41 \,\mathrm{mag}, \Delta B = 5.55 \,\mathrm{mag}, \Delta V = 4.53 \,\mathrm{mag}, \Delta R = 5.80 \,\mathrm{mag}$, and $\Delta I = 5.34 \,\mathrm{mag}$. The average color indices are: $U-B =-0.54 \pm 0.18 \,\mathrm{mag}, B-V = 0.56 \pm 0.21 \,\mathrm{mag}, B-R = 0.93 \pm 0.18 \,\mathrm{mag}, B-I = 1.51 \pm 0.24 \,\mathrm{mag}, V-R = 0.44 \pm 0.15 \,\mathrm{mag}$, and $V-I = 1.03 \pm 0.23 \,\mathrm{mag}$. 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.

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