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Authors: Reeves, J. N.
Porquet, D.
Braito, V.
Nardini, E.
Lobban, A.
Turner, T. J.
First Published: 8-Sep-2016
Publisher: American Astronomical Society, IOP Publishing
Citation: The Astrophysical Journal, 828:98 (21pp), 2016 September 10
Abstract: The Seyfert 1 galaxy Ark 120 is a prototype example of the so-called class of bare nucleus active galactic nuclei (AGNs), whereby there is no known evidence for the presence of ionized gas along the direct line of sight. Here deep (>400 ks exposure), high-resolution X-ray spectroscopy of Ark 120 is presented from XMM-Newton observations that were carried out in 2014 March, together with simultaneous Chandra/High Energy Transmission Grating exposures. The high-resolution spectra confirmed the lack of intrinsic absorbing gas associated with Ark 120, with the only X-ray absorption present originating from the interstellar medium (ISM) of our own Galaxy, with a possible slight enhancement of the oxygen abundance required with respect to the expected ISM values in the solar neighborhood. However, the presence of several soft X-ray emission lines are revealed for the first time in the XMM-Newton RGS spectrum, associated with the AGN and arising from the He- and H-like ions of N, O, Ne, and Mg. The He-like line profiles of N, O, and Ne appear velocity broadened, with typical FWHMs of ~5000 km s−1, whereas the H-like profiles are unresolved. From the clean measurement of the He-like triplets, we deduce that the broad lines arise from a gas of density n e ~ 1011 cm−3, while the photoionization calculations infer that the emitting gas covers at least 10% of 4π steradian. Thus the broad soft X-ray profiles appear coincident with an X-ray component of the optical–UV broad-line region on sub-parsec scales, whereas the narrow profiles originate on larger parsec scales, perhaps coincident with the AGN narrow-line region. The observations show that Ark 120 is not intrinsically bare and substantial X-ray-emitting gas exists out of our direct line of sight toward this AGN.
DOI Link: 10.3847/0004-637X/828/2/98
ISSN: 1538-4357
Version: Publisher Version
Status: Peer-reviewed
Type: Journal Article
Rights: Archived with reference to SHERPA/RoMEO and publisher website.
Appears in Collections:Published Articles, Dept. of Physics and Astronomy

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