Spectral Density of the Possibly Random Fluctuations of 3C 273

Abstract

THE possible existence of a long term periodicity in the fluctuations of optical luminosity of quasi-stellar radio sources has been a subject of considerable debate. On the basis of the compilation of 3C 273 data of Smith and Hoffleit¹, Smith² has suggested a periodicity of about 13 years. From a similar compilation, Geyer³ found evidence for a periodicity of about 15 years. Ozernoi and Chertoprud⁴ averaged the data of Smith and Hoffleit over 2 year intervals to remove the short term fluctuations and found that the best fit of the data by a single sinusoid was for a periodicity of 9 ± 1.2 yr. A common technique used to study the harmonic content of a signal is to find its spectral density, which is the Fourier transform of the auto-correlation function of the signal. To study further the possible existence of a periodicity in the observed fluctuations, we have calculated their spectral density and we shall now show here that qualitatively similar spectral density distributions are obtained from simulated luminosity curves which were constructed with random amplitude fluctuations.