A deep X-ray view of the bare AGN Ark 120. III. X-ray timing analysis and multiwavelength variability
Date Issued
2018
Author(s)
Abstract
We present the spectral/timing properties of the bare Seyfert galaxy Ark 120
through a deep ~420ks XMM-Newton campaign plus recent NuSTAR observations and a
~6-month Swift monitoring campaign. We investigate the spectral decomposition
through fractional rms, covariance and difference spectra, finding the mid- to
long-timescale (~day-year) variability to be dominated by a relatively smooth,
steep component, peaking in the soft X-ray band. Additionally, we find evidence
for variable FeK emission red-ward of the FeK-alpha core on long timescales,
consistent with previous findings. We detect a clearly-defined power spectrum
which we model with a power law with a slope of alpha ~ 1.9. By extending the
power spectrum to lower frequencies through the inclusion of Swift and RXTE
data, we find tentative evidence of a high-frequency break, consistent with
existing scaling relations. We also explore frequency-dependent Fourier time
lags, detecting a negative ('soft') lag for the first time in this source with
the 0.3-1 keV band lagging behind the 1-4 keV band with a time delay of ~900s.
Finally, we analyze the variability in the optical and UV bands using the
Optical/UV Monitor on-board XMM-Newton and the UVOT on-board Swift and search
for time-dependent correlations between the optical/UV/X-ray bands. We find
tentative evidence for the U-band emission lagging behind the X-rays with a
time delay of 2.4 +/- 1.8 days, which we discuss in the context of disc
reprocessing.
Volume
474
Issue
3
Start page
3237
Issn Identifier
0035-8711
Ads BibCode
2018MNRAS.474.3237L
Rights
open.access
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