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|Title:||A deep X-ray view of the bare AGN Ark 120. IV. XMM-Newton and NuSTAR spectra dominated by two temperature (warm, hot) Comptonization processes||Authors:||Porquet, D.
Reeves, J. N.
Ballantyne, D. R.
Boggs, S. E.
Christensen, F. E.
Hailey, C. J.
Zhang, W. W.
|Issue Date:||2018||Journal:||ASTRONOMY & ASTROPHYSICS||Number:||609||First Page:||A42||Abstract:||Context. The physical characteristics of the material closest to supermassive black holes (SMBHs) are primarily studied through X-ray observations. However, the origins of the main X-ray components such as the soft X-ray excess, the Fe Kα line complex, and the hard X-ray excess are still hotly debated. This is particularly problematic for active galactic nuclei (AGN) showing a significant intrinsic absorption, either warm or neutral, which can severely distort the observed continuum. Therefore, AGN with no (or very weak) intrinsic absorption along the line of sight, so-called "bare AGN", are the best targets to directly probe matter very close to the SMBH. <BR /> Aims: We perform an X-ray spectral analysis of the brightest and cleanest bare AGN known so far, Ark 120, in order to determine the process(es) at work in the vicinity of the SMBH. <BR /> Methods: We present spectral analyses of data from an extensive campaign observing Ark 120 in X-rays with XMM-Newton (4 × 120 ks, 2014 March 18-24), and NuSTAR (65.5 ks, 2014 March 22). <BR /> Results: During this very deep X-ray campaign, the source was caught in a high-flux state similar to the earlier 2003 XMM-Newton observation, and about twice as bright as the lower-flux observation in 2013. The spectral analysis confirms the "softer when brighter" behavior of Ark 120. The four XMM-Newton/pn spectra are characterized by the presence of a prominent soft X-ray excess and a significant Fe Kα complex. The continuum is very similar above about 3 keV, while significant variability is present for the soft X-ray excess. We find that relativistic reflection from a constant-density, flat accretion disk cannot simultaneously produce the soft excess, broad Fe Kα complex, and hard X-ray excess. Instead, Comptonization reproduces the broadband (0.3-79 keV) continuum well, together with a contribution from a mildly relativistic disk reflection spectrum. <BR /> Conclusions: During this 2014 observational campaign, the soft X-ray spectrum of Ark 120 below 0.5 keV was found to be dominated by Comptonization of seed photons from the disk by a warm (kT<SUB>e</SUB> 0.5 keV), optically-thick corona (τ 9). Above this energy, the X-ray spectrum becomes dominated by Comptonization from electrons in a hot optically thin corona, while the broad Fe Kα line and the mild Compton hump result from reflection off the disk at several tens of gravitational radii.||URI:||http://hdl.handle.net/20.500.12386/28409||URL:||https://www.aanda.org/articles/aa/abs/2018/01/aa31290-17/aa31290-17.html||ISSN:||0004-6361||DOI:||10.1051/0004-6361/201731290||Bibcode ADS:||2018A&A...609A..42P||Fulltext:||open|
|Appears in Collections:||1.01 Articoli in rivista|
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checked on Jan 19, 2021
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