How Far Is Quasar UV/Optical Variability from a Damped Random Walk at Low Frequency?

Studies have shown that UV/optical light curves of quasars can be described using the prevalent damped random walk (DRW) model, also known as the Ornstein-Uhlenbeck process. A white noise power spectral density (PSD) is expected at low frequency in this model; however, a direct observational constra...

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Bibliographic Details
Published inThe Astrophysical journal Vol. 847; no. 2; pp. 132 - 141
Main Authors Guo, Hengxiao, Wang, Junxian, Cai, Zhenyi, Sun, Mouyuan
Format Journal Article
LanguageEnglish
Published Philadelphia The American Astronomical Society 01.10.2017
IOP Publishing
Subjects
Astrophysics
ASTROPHYSICS, COSMOLOGY AND ASTRONOMY
Computer simulation
Constraint modelling
GALAXIES
galaxies: active
Light curve
Low frequencies
MAGNETIC FIELDS
METALLICITY
NOISE
Parameter uncertainty
Physical factors
Power spectral density
QUASARS
quasars: general
Random walk
RANDOMNESS
Scattering
SIMULATION
Slopes
SPECTRAL DENSITY
STARS
VARIATIONS
VISIBLE RADIATION
White noise
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Summary:Studies have shown that UV/optical light curves of quasars can be described using the prevalent damped random walk (DRW) model, also known as the Ornstein-Uhlenbeck process. A white noise power spectral density (PSD) is expected at low frequency in this model; however, a direct observational constraint to the low-frequency PSD slope is difficult due to the limited lengths of the light curves available. Meanwhile, quasars show scatter in their DRW parameters that is too large to be attributed to uncertainties in the measurements and dependence on the variation of known physical factors. In this work we present simulations showing that, if the low-frequency PSD deviates from the DRW, the red noise leakage can naturally produce large scatter in the variation parameters measured from simulated light curves. The steeper the low-frequency PSD slope, the larger scatter we expect. Based on observations of SDSS Stripe 82 quasars, we find that the low-frequency PSD slope should be no steeper than −1.3. The actual slope could be flatter, which consequently requires that the quasar variabilities should be influenced by other unknown factors. We speculate that the magnetic field and/or metallicity could be such additional factors.
Bibliography:Galaxies and Cosmology
AAS07033
ISSN:0004-637X
1538-4357
DOI:10.3847/1538-4357/aa8d71