Measuring the Variability in K2 Optical Light Curves of the Binary Black Hole Candidate OJ 287 and Other Fermi Active Galactic Nuclei in 2014–2015

Abstract

We characterize the variability in nearly continuous optical observations of nine active galactic nuclei (AGNs) detected with the Fermi Gamma Ray Space Telescope Large Area Telescope (Fermi-LAT), obtained during the K2 mission with the Kepler spacecraft with 1-minute or 30-minute cadences. The binary black hole candidate OJ 287, six other γ-ray blazars, the lobe-dominated radio quasar 3C 207, and the X-ray- bright quasar RBS 1273 were observed. The most dramatic variability was seen in PKS 1352-104, which varied by a factor of six in 4 days. OJ 287 varied by a factor of 2.8, six other blazars varied by factors of 1.14-2.23, and RBS 1273 varied by a factor of only 1.03. Power spectral densities (PSDs) were calculated for each object. Six of the nine AGNs were detected by the Fermi-LAT during the K2 observations. The slopes of the PSDs for these six contemporaneously detected AGNs were not significantly different from the slopes of the three contemporaneously undetected AGNs. The PSD slopes of the three BL Lac objects and the four flat-spectrum radio quasars were not significantly different, consistent with the relativistic jet acting as the dominant source of the emission in both subclasses of blazars. Overall, the slopes of most PSDs are consistent with turbulence in the relativistic jet, but the steepest PSDs require the addition of another mechanism that produces additional flux variations on timescales of several days during major flaring episodes.