Active Galactic Nuclei Discovered in the Kepler Mission

TL;DR

This study identifies candidate active galactic nuclei (AGN) in Kepler data by analyzing brightness variations in about 500 galaxies, revealing variability patterns and potential quasi-periodic behavior over several years.

Contribution

It presents new techniques for detecting and analyzing AGN variability in Kepler light curves, including mitigation of instrumental trends and structure function analysis.

Findings

Approximately 4% of sampled galaxies show continuous variability.

Variability amplitudes increase with longer timescales.

Some candidates exhibit features suggestive of quasi-periodic behavior.

Abstract

We report on candidate active galactic nuclei (AGN) discovered during the monitoring of $\sim$500 bright (r < 18 mag) galaxies over several years with the Kepler Mission. Most of the targets were sampled every 30 minutes nearly continuously for a year or more. Variations of 0.001 mag and often less could be detected reliably. About 4.0% (19) of our random sample continuously fluctuated with amplitudes increasing with longer timescales, but the majority are close to the limits of detectability with Kepler. We discuss our techniques to mitigate the long term instrumental trends in Kepler light curves and our resulting structure function curves. The amplitudes of variability over four month periods, as seen in the structure functions and PSDs, can dramatically change for many of these AGN candidates. Four of the candidates have features in their Structure Functions that may indicate quasi-periodic behavior, although other possibilities are discussed.