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Title: Discovery of a ∼5 day characteristic timescale in the Kepler power spectrum of Zw 229–15

We present time series analyses of the full Kepler data set of Zw 229–15. This Kepler light curve—with a baseline greater than 3 yr, composed of virtually continuous, evenly sampled 30 minute measurements—is unprecedented in its quality and precision. We utilize two methods of power spectral analysis to investigate the optical variability and search for evidence of a bend frequency associated with a characteristic optical variability timescale. Each method yields similar results. The first interpolates across data gaps to use the standard Fourier periodogram. The second, using the CARMA-based time-domain modeling technique of Kelly et al., does not need evenly sampled data. Both methods find excess power at high frequencies that may be due to Kepler instrumental effects. More importantly, both also show strong bends (Δα ∼ 2) at timescales of ∼5 days, a feature similar to those seen in the X-ray power spectral densities of active galactic nuclei (AGNs) but never before in the optical. This observed ∼5 day timescale may be associated with one of several physical processes potentially responsible for the variability. A plausible association could be made with light-crossing dynamical or thermal timescales depending on the assumed value of the accretion disk size and on unobservedmore » disk parameters such as α and H/R. This timescale is not consistent with the viscous timescale, which would be years in a ∼10{sup 7} M {sub ☉} AGN such as Zw 229–15. However, there must be a second bend on long (≳ 1 yr) timescales and that feature could be associated with the viscous timescale.« less
Authors:
; ;  [1] ;  [2] ;  [3] ;  [4] ;  [5]
  1. Department of Astronomy, University of Maryland, College Park, MD 20742-2421 (United States)
  2. X-Ray and Observational Astronomy Group, Department of Physics and Astronomy, University of Leicester, University Road, Leicester LE1 7RH (United Kingdom)
  3. Department of Physics and Astronomy, University of California, Los Angeles, CA 90095-1547 (United States)
  4. Department of Physics, Broida Hall, University of California, Santa Barbara, CA 93106-9530 (United States)
  5. Astrophysics Science Division, NASA/GSFC, Code 660, Greenbelt, MD 20771 (United States)
Publication Date:
OSTI Identifier:
22370352
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 795; Journal Issue: 1; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCRETION DISKS; ACCURACY; BLACK HOLES; GALAXIES; GALAXY NUCLEI; SIMULATION; SPECTRA; SPECTRAL DENSITY; TIME-SERIES ANALYSIS; VISIBLE RADIATION; X RADIATION