# The optical variability of Supermassive Black Hole Binary Candidate PG1302-102: Periodicity and perturbation in the light curve

## TL;DR

This study models the optical light curve of PG1302-102, a supermassive black hole binary candidate, showing that perturbations can explain observed periodicity fluctuations and predicting a slightly longer period consistent with observations.

## Contribution

The paper introduces a physical model with disk perturbations that explains the light curve variability and period fluctuations of PG1302-102, supporting its binary black hole nature.

## Key findings

- Model reproduces observed light curve with perturbation.
- Predicted period of about 1899 days aligns with observations.
- Periodic fluctuations are confirmed by hybrid periodicity detection.

## Abstract

The photometric light curve of PG1302-102 shows periodic variability which makes this object one of the most plausible supermassive black hole binary candidate. Interestingly, the most recent study of its updated optical light curve reports a decrease in 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 years, with a supermassive black hole binary system in which a perturbation in the accretion disk of 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 due to a cold spot in the disk of {\bf more massive} component of a close, unequal-mass ($\frac{\mathrm{m}_{1}}{\mathrm{m}_{2}}=0.1$) black hole binary system. The light curve resembles the pattern of 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 ($1972\pm 254$ days) and modeled ($1873 \pm \ 250$ days) light curves are within one-sigma, 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 PG1302-102 is evident from our physical model and confirmed by the hybrid method for periodicity detection.