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Pan-STARRS1 variability of XMM-COSMOS AGN. II. Physical correlations and power spectrum analysis | | T. Simm
; M. Salvato
; R. Saglia
; G. Ponti
; G. Lanzuisi
; K. Nandra
; R. Bender
; | | Date: |
22 Oct 2015 | | Abstract: | [Abbreviated] We search for scaling relations between the fundamental AGN
parameters and rest-frame UV/optical variability properties for a sample of
$sim$90 X-ray selected AGNs covering a wide redshift range from the XMM-COSMOS
survey, with optical light curves in four bands provided by the Pan-STARRS1
(PS1) Medium Deep Field 04 survey. To estimate the variability amplitude we
utilize the normalized excess variance ($sigma_{mathrm{rms}}^{2}$) and probe
variability on rest-frame timescales of several months and years by calculating
$sigma_{mathrm{rms}}^{2}$ from different parts of our light curves. In
addition, we derive the rest-frame optical PSD for our sources using
continuous-time autoregressive moving average (CARMA) models. We observe that
the excess variance and the PSD amplitude are strongly anti-correlated with
wavelength, bolometric luminosity and Eddington ratio. There is no evidence for
a dependency of the variability amplitude on black hole mass and redshift.
These results suggest that the accretion rate is the fundamental physical
quantity determining the rest-frame UV/optical variability amplitude of quasars
on timescales of months and years. The optical PSD of all of our sources is
consistent with a broken power law showing a characteristic bend at rest-frame
timescales ranging between $sim$100 and $sim$300 days. The break timescale
exhibits no significant correlation with any of the fundamental AGN parameters.
The low frequency slope of the PSD is consistent with a value of $-1$ for most
of our objects, whereas the high frequency slope is characterized by a broad
distribution of values between $sim-2$ and $sim-4$. These findings unveil
significant deviations from the simple "damped random walk" model, frequently
used in previous optical variability studies. We find a weak tendency for AGNs
with higher black hole mass having steeper high frequency PSD slopes. | | Source: | arXiv, 1510.6737 | | Services: | Forum | Review | PDF | Favorites | |
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