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Are the variability properties of the Kepler AGN light curves consistent with a damped random walk?
Journal article   Open access

Are the variability properties of the Kepler AGN light curves consistent with a damped random walk?

Vishal P. Kasliwal, Michael S. Vogeley and Gordon T. Richards
Monthly notices of the Royal Astronomical Society, v 451(4), pp 4328-4345
21 Aug 2015
DOI: https://doi.org/10.1093/mnras/stv1230
url
https://doi.org/10.1093/mnras/stv1230View
SubmittedOpen Access (License Unspecified),  Open

Abstract

Astronomy & Astrophysics Physical Sciences Science & Technology
We test the consistency of active galactic nuclei (AGN) optical flux variability with the damped random walk (DRW) model. Our sample consists of 20 multiquarter Kepler AGN light curves including both Type 1 and 2 Seyferts, radio-loud and -quiet AGN, quasars, and blazars. Kepler observations of AGN light curves offer a unique insight into the variability properties of AGN light curves because of the very rapid (11.6-28.6 min) and highly uniform rest-frame sampling combined with a photometric precision of 1 part in 10(5) over a period of 3.5 yr. We categorize the light curves of all 20 objects based on visual similarities and find that the light curves fall into five broad categories. We measure the first-order structure function of these light curves and model the observed light curve with a general broken power-law power spectral density (PSD) characterized by a short-time-scale power-law index gamma and turnover time-scale tau. We find that less than half the objects are consistent with a DRW and observe variability on short time-scales (similar to 2 h). The turnover time-scale tau ranges from similar to 10-135 d. Interesting structure function features include pronounced dips on rest-frame time-scales ranging from 10-100 d and varying slopes on different time-scales. The range of observed short-time-scale PSD slopes and the presence of dip and varying slope features suggests that the DRW model may not be appropriate for all AGN. We conclude that AGN variability is a complex phenomenon that requires a more sophisticated statistical treatment.

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