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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

Porquet, D. and Reeves, J. N. and Matt, G. and Marinucci, A. and Nardini, E. and Braito, V. and Lobban, A. and Ballantyne, D. R. and Boggs, S. E. and Christensen, F. E. and Dauser, T. and Farrah, D. and García, J. and Hailey, C. J. and Harrison, F. and Stern, D. and Tortosa, A. and Ursini, F. and Zhang, W. W. (2018) 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. Astronomy and Astrophysics, 609 . Art. No. A42. ISSN 0004-6361.

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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. 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. 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). 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. 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 (kTe ~ 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.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Porquet, D.0000-0001-9731-0352
Matt, G.0000-0002-2152-0916
Nardini, E.0000-0001-9226-8992
Braito, V.0000-0002-2629-4989
Lobban, A.0000-0002-6433-1357
Ballantyne, D. R.0000-0001-8128-6976
Boggs, S. E.0000-0001-9567-4224
Christensen, F. E.0000-0001-5679-1946
Dauser, T.0000-0003-4583-9048
Farrah, D.0000-0003-1748-2010
García, J.0000-0003-3828-2448
Harrison, F.0000-0003-2992-8024
Stern, D.0000-0003-2686-9241
Zhang, W. W.0000-0002-1426-9698
Additional Information:© 2018 ESO. Article published by EDP Sciences. Received 1 June 2017; Accepted 24 July 2017; Published online 05 January 2018. The authors would like to deeply thank the anonymous referee for useful and constructive comments. The paper is based on observations obtained with the XMM-Newton, and ESA science mission with instruments and contributions directly funded by ESA member states and the USA (NASA). This work made use of data from the NuSTAR mission, a project led by the California Institute of Technology, managed by the Jet Propulsion Laboratory, and funded by NASA. This research has made use of the NuSTAR Data Analysis Software (NuSTARDAS) jointly developed by the ASI Science Data Center and the California Institute of Technology. D.P. would like to acknowledge financial support from the French “Programme National Hautes Énergies” (PNHE). Part of the work was supported by the European Union Seventh Framework Program under the grant agreement No. 312789 (D.P., G.M., A.M., A.F.). J.N.R. acknowledges financial support via Chandra grant number GO4-15092X and NASA grant NNX15AF12G. J.N.R. and A.L. also acknowledge the support of the STFC, via the consolidated grant ST/M001040/1. G.M., A.M., A.T. and F.U. acknowledge financial support from the Italian Space Agency under grant ASI/INAF I/037/12/0-011/13. E.N. acknowledges funding from the European Union’s Horizon 2020 research and innovation program under the Marie Sklodowska-Curie grant agreement No. 664931.
Group:NuSTAR, Space Radiation Laboratory, Astronomy Department
Funding AgencyGrant Number
Programme National Hautes Énergies (PNHE)UNSPECIFIED
European Research Council (ERC)312789
Science and Technology Facilities Council (STFC)ST/M001040/1
Agenzia Spaziale Italiana (ASI)I/037/12/0-011/13
Marie Curie Fellowship664931
Subject Keywords:X-rays: individuals: Ark 120 – galaxies: active – radiation mechanisms: general – accretion, accretion disks – quasars: general
Record Number:CaltechAUTHORS:20180125-144741618
Persistent URL:
Official Citation: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. D. Porquet, J. N. Reeves, G. Matt, A. Marinucci, E. Nardini, V. Braito, A. Lobban, D. R. Ballantyne, S. E. Boggs, F. E. Christensen, T. Dauser, D. Farrah, J. Garcia, C. J. Hailey, F. Harrison, D. Stern, A. Tortosa, F. Ursini and W. W. Zhang. A&A, 609 (2018) A42. DOI:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:84530
Deposited By: Tony Diaz
Deposited On:30 Jan 2018 12:15
Last Modified:17 Dec 2019 22:00

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