A deep X-ray view of the bare AGN Ark 120. III. X-ray timing analysis and multiwavelength variability

作者：Lobban A. P.^*; Porquet D.; Reeves J. N.; Markowitz A.; Nardini E.; Grosso N.

来源：Monthly Notices of the Royal Astronomical Society, 2018, 474(3): 3237-3258.

DOI：10.1093/mnras/stx2889

• accretion, accretion discs
• galaxies: active
• galaxies: Seyfert
• X-rays: galaxies

We present the spectral/timing properties of the bare Seyfert galaxy Ark 120 through a deep similar to 420 ks XMM-Newton campaign plus recent NuSTAR observations and a similar to 6-month Swift monitoring campaign. We investigate the spectral decomposition through fractional rms, covariance and difference spectra, finding the mid-to long-time-scale (similar to 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 redward of the FeK alpha core on long time-scales, consistent with previous findings. We detect a clearly defined power spectrum which we model with a power law with a slope of alpha similar to 1.9. By extending the power spectrum to lower frequencies through the inclusion of Swift and Rossi X-ray Timing Explorer 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, tau, of similar to 900 s. Finally, we analyse the variability in the optical and ultraviolet (UV) bands using the Optical/UV Monitor onboard XMM-Newton and the Ultra-Violet/Optical Telescope onboard 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 tau = 2.4 +/- 1.8 d, which we discuss in the context of disc reprocessing.

• 出版日期2018-3