http://arxiv.org/abs/1604.05858
Discrepancies between reported structure function (SF) slopes and their overall flatness as compared to expectations from the damped random walk (DRW) model, generally well-describing the variability of active galactic nuclei (AGN), has triggered us to study this problem in detail. We review common AGN variability observables and identify their most common problems. Equipped with this knowledge, we study ~9000 r-band AGN light curves from Stripe 82 of the Sloan Digital Sky Survey, using SFs described by stochastic processes with the power exponential covariance matrix of the signal. We model the “sub-ensemble” SFs in the redshift-absolute magnitude bins with the full SF equation (including the turnover and the noise part) and a single power-law (SPL; in the “red noise regime” after subtracting the noise term). The distribution of full-equation SF (SPL) slopes peaks at gamma=0.55+/-0.08 (0.52+/-0.06) and is consistent with DRW. There is a hint of a weak correlation of gamma with the luminosity and a lack of correlation with the black hole mass. The typical decorrelation time scale in optical is tau=0.97+\-0.46 year. The SF amplitude at one year obtained from the SPL fitting is SF_0=0.22+/-0.06 mag and is overestimated because SF is already at the turnover part, hence the true value is SF_0=0.20+/-0.06 mag. The asymptotic variability is SF_\infty=0.25+/-0.06 mag. It is strongly anti-correlated with both the luminosity and Eddington ratio, and is correlated with the black hole mass. The reliability of these results is fortified with Monte Carlo simulations.
S. Kozlowski
Thu, 21 Apr 16
49/61
Comments: 16 pages, 11 figures, ApJ submitted – after the first positive referee report; comments welcome
You must be logged in to post a comment.