Evidence for an Optical Low-frequency Quasi-Periodic Oscillation in the Kepler Light Curve of an Active Galaxy

TL;DR

This paper presents evidence of a low-frequency quasi-periodic oscillation in the optical light curve of an active galaxy, suggesting a potential universal correlation between QPO frequency and black hole mass across different scales.

Contribution

The study reports the first detection of a low-frequency QPO in an AGN's optical light curve and links it to known correlations across black hole systems, using a novel Kepler data analysis pipeline.

Findings

Detected a 44-day QPO in the optical light curve of an AGN.

Found the QPO frequency aligns with the black hole mass correlation.

Supports the universality of QPO phenomena across black hole systems.

Abstract

We report evidence for a quasi-periodic oscillation (QPO) in the optical light curve of KIC 9650712, a narrow-line Seyfert 1 galaxy in the original Kepler field. After the development and application of a pipeline for Kepler data specific to active galactic nuclei (AGN), one of our sample of 21 AGN selected by infrared photometry and X-ray flux demonstrates a peak in the power spectrum at log $\nu$ = -6.58 Hz, corresponding to a temporal period of t=44 days. We note that although the power spectrum is well-fit by a model consisting of a Lorentzian and a single power law, alternative continuum models cannot be ruled out. From optical spectroscopy, we measure the black hole mass of this AGN as log $M_{\mathrm{BH}} / M_\odot$ = 8.17. We find that this frequency lies along a correlation between low-frequency QPOs and black hole mass from stellar and intermediate mass black holes to AGN, similar to the known correlation in high-frequency QPOs.