The Optical Variability of Supermassive Black Hole Binary Candidate PG 1302–102: Periodicity and Perturbation in the Light Curve

Abstract

The photometric light curve of PG 1302–102 shows periodic variability, which makes this object one of the most plausible supermassive black hole binary candidates. Interestingly, the most recent study of its updated optical light curve reports a decrease in the significance of periodicity, which may suggest that the binary model is less favorable. Here we model the PG 1302–102 light curve, spanning almost 20 yr, with a supermassive black hole binary system in which a perturbation in the accretion disk of a more massive component is present. Our model reproduces well the observed light curve, with a slight perturbation of a sinusoidal feature, and predicts that a slightly larger period than previously reported, of about 1899 days, could arise owing to a cold spot in the disk of a more massive component of a close, unequal-mass ( ) black hole binary system. The light curve resembles the pattern of a sinusoid-like shape within a few years, which could be confirmed by future observations. In addition, using our hybrid method for periodicity detection, we show that the periods in the observed (1972 ± 254 days) and modeled (1873 ± 250 days) light curves are within 1 σ , which is also consistent with our physical model prediction and with previous findings. Thus, both the periodic nature and its slight fluctuation of the light curve of PG 1302–102 are evident from our physical model and confirmed by the hybrid method for periodicity detection.