Energy-dependent variability of the bare Seyfert 1 galaxy Ark 120

Abstract

We present results from a detailed spectral-timing analysis of a long ~486 ks XMM-Newton observation of the bare Seyfert 1 galaxy Ark 120 which showed alternating diminution and increment in the 0.3-10 keV X-ray flux over four consecutive orbits in 2014. We study the energy-dependent variability of Ark 120 through broad-band X-ray spectroscopy, fractional root-mean-squared (rms) spectral modelling, hardness-intensity diagram and flux-flux analysis. The X-ray (0.3-10 keV) spectra are well fitted by a thermally Comptonized primary continuum with two (blurred and distant) reflection components and an optically thick, warm Comptonization component for the soft X-ray excess emission below ~2 keV. During the first and third observations, the fractional X-ray variability amplitude decreases with energy while for second and fourth observations, X-ray variability spectra are found to be inverted-crescent and crescent shaped respectively. The rms variability spectra are well modelled by two constant reflection components, a soft excess component with variable luminosity and a variable intrinsic continuum with the normalization and spectral slope being correlated. The spectral softening of the source with both the soft excess and UV luminosities favour Comptonization models where the soft excess and primary X-ray emission are produced through Compton up-scattering of the UV and UV/soft X-ray seed photons in the putative warm and hot coronae, respectively. Our analyses imply that the observed energy-dependent variability of Ark 120 is most likely due to variations in the spectral shape and luminosity of the hot corona and to variations in the luminosity of the warm corona, both of which are driven by variations in the seed photon flux.

17 pages, 19 figures, 6 tables, accepted for publication in MNRAS

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• Modelling X-ray RMS spectra I: intrinsically variable AGN
• A deep X-ray view of the bare AGN Ark 120. III. X-ray timing analysis and multiwavelength variability
• High-density disc reflection spectroscopy of low-mass active galactic nuclei
• Classifying AGN by X-ray Hardness Variability
• Detection of the high energy cut-off from the Seyfert 1.5 galaxy NGC 5273
• Exploring the spectral variability of the Seyfert 1.5 galaxy Markarian 530 with Suzaku
• Modelling X-ray RMS spectra II: the ultra-fast outflow of PDS 456
• Large-amplitude rapid X-ray variability in the narrow-line Seyfert 1 galaxy PG 1404$+$226