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: ΔU = 4.41 mag, ΔB = 5.55 mag, ΔV = 4.53 mag, ΔR = 5.80mag, and ΔI = 5.34 mag. The average color indices are: U - B = -0.54±0.18mag, B - V = 0.56±0.21 mag, B - R = 0.93±0.18 mag, B - I= 1.51±0.24mag, V - R = 0.44±0.15 mag, and V - I = 1.03±0.23 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. © 2006. Astronomical Society of Japan.