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Space telescope and optical reverberation mapping project. X. Understanding the absorption-line holiday in NGC 5548

Space telescope and optical reverberation mapping project. X. Understanding the absorption-line holiday in NGC 5548
Space telescope and optical reverberation mapping project. X. Understanding the absorption-line holiday in NGC 5548
The flux variations in the emission lines in active galactic nuclei (AGNs) are driven by variations in the ionizing continuum flux - which are usually reflected in the observable UV-optical continuum. The "Reverberation mapping" technique measures the delay between line and continuum variations to determine the size of the line emitting region, this is the basis for measurements of the central black hole mass inAGNs. The Space Telescope and Optical Reverberation Mapping Project (AGNSTORM) on NGC 5548 in 2014 is the most intensive multi-wavelength AGN monitoring campaign ever. For most of the campaign, the emission-line variations followed changes in the continuum with a time lag, as expected. However, the lines varied independently of the observed UV-optical continuum during a 60 - 70 day "holiday." To understand this remarkable phenomenon, we study the intrinsic absorption lines present in NGC 5548. We identify a novel cycle that reproduces the absorption line variability and thus identify the physics that allows the holiday to occur. In our model, variations in this obscurer's line-of-sight covering factor modify the soft X-ray continuum. This leads to changes in the ionization of helium gas in the broad-line region. Ionizing radiation produced by recombining helium then affects the ionization of other species as observed during the AGN STORM holiday. It is likely that any other model which selectively changes the soft X-ray part of the continuum during the holiday can also explain the anomalous emission line behavior observed.
Astrophysics - Astrophysics of Galaxies
0004-637X
1-10
Dehghanian, M.
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Ferland, G.J.
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Kriss, G.A.
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Peterson, B.M.
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Mathur, S.
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Mehdipour, M.
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Guzman, F.
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Chatzikos, M.
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Van Hoof, P.A.M.
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Williams, R.J.R.
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Arav, N.
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Barth, A.J.
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Bentz, M.C.
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Bisogni, S.
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Brandt, W.N.
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Crenshaw, D.M.
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Dalla Bonta, E.
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De Rosa, G.
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Fausnaugh, M.M.
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Gelbord, J. M.
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Goad, M.R.
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Gupta, A.
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Horne, K.
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Kaastra, J.
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Knigge, C.
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Korista, K.T.
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Mc Hardy, I. M.
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Pogge, R.W.
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Starkey, D.A.
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Vestergaard, M.
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Dehghanian, M.
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Ferland, G.J.
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Kriss, G.A.
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Peterson, B.M.
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Mathur, S.
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Mehdipour, M.
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Guzman, F.
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Chatzikos, M.
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Van Hoof, P.A.M.
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Williams, R.J.R.
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Arav, N.
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Barth, A.J.
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Bentz, M.C.
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Bisogni, S.
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Brandt, W.N.
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Crenshaw, D.M.
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Dalla Bonta, E.
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De Rosa, G.
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Fausnaugh, M.M.
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Gelbord, J. M.
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Goad, M.R.
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Gupta, A.
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Horne, K.
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Kaastra, J.
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Knigge, C.
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Korista, K.T.
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Mc Hardy, I. M.
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Pogge, R.W.
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Starkey, D.A.
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Vestergaard, M.
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Dehghanian, M., Ferland, G.J., Kriss, G.A., Peterson, B.M., Mathur, S., Mehdipour, M., Guzman, F., Chatzikos, M., Van Hoof, P.A.M., Williams, R.J.R., Arav, N., Barth, A.J., Bentz, M.C., Bisogni, S., Brandt, W.N., Crenshaw, D.M., Dalla Bonta, E., De Rosa, G., Fausnaugh, M.M., Gelbord, J. M., Goad, M.R., Gupta, A., Horne, K., Kaastra, J., Knigge, C., Korista, K.T., Mc Hardy, I. M., Pogge, R.W., Starkey, D.A. and Vestergaard, M. (2019) Space telescope and optical reverberation mapping project. X. Understanding the absorption-line holiday in NGC 5548. The Astrophysical Journal, 887 (2), 1-10, [119]. (doi:10.3847/1538-4357/ab1b48).

Record type: Article

Abstract

The flux variations in the emission lines in active galactic nuclei (AGNs) are driven by variations in the ionizing continuum flux - which are usually reflected in the observable UV-optical continuum. The "Reverberation mapping" technique measures the delay between line and continuum variations to determine the size of the line emitting region, this is the basis for measurements of the central black hole mass inAGNs. The Space Telescope and Optical Reverberation Mapping Project (AGNSTORM) on NGC 5548 in 2014 is the most intensive multi-wavelength AGN monitoring campaign ever. For most of the campaign, the emission-line variations followed changes in the continuum with a time lag, as expected. However, the lines varied independently of the observed UV-optical continuum during a 60 - 70 day "holiday." To understand this remarkable phenomenon, we study the intrinsic absorption lines present in NGC 5548. We identify a novel cycle that reproduces the absorption line variability and thus identify the physics that allows the holiday to occur. In our model, variations in this obscurer's line-of-sight covering factor modify the soft X-ray continuum. This leads to changes in the ionization of helium gas in the broad-line region. Ionizing radiation produced by recombining helium then affects the ionization of other species as observed during the AGN STORM holiday. It is likely that any other model which selectively changes the soft X-ray part of the continuum during the holiday can also explain the anomalous emission line behavior observed.

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1812.11578v2 - Accepted Manuscript
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Dehghanian 2019 ApJ 877 119 - Version of Record
Available under License Creative Commons Attribution.
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Accepted/In Press date: 20 April 2019
e-pub ahead of print date: 3 June 2019
Published date: June 2019
Keywords: Astrophysics - Astrophysics of Galaxies

Identifiers

Local EPrints ID: 427238
URI: http://eprints.soton.ac.uk/id/eprint/427238
ISSN: 0004-637X
PURE UUID: ed68ef9c-a2a7-4cea-9aa6-0e7575368230

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Date deposited: 09 Jan 2019 17:30
Last modified: 21 Nov 2021 14:57

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Contributors

Author: M. Dehghanian
Author: G.J. Ferland
Author: G.A. Kriss
Author: B.M. Peterson
Author: S. Mathur
Author: M. Mehdipour
Author: F. Guzman
Author: M. Chatzikos
Author: P.A.M. Van Hoof
Author: R.J.R. Williams
Author: N. Arav
Author: A.J. Barth
Author: M.C. Bentz
Author: S. Bisogni
Author: W.N. Brandt
Author: D.M. Crenshaw
Author: E. Dalla Bonta
Author: G. De Rosa
Author: M.M. Fausnaugh
Author: J. M. Gelbord
Author: M.R. Goad
Author: A. Gupta
Author: K. Horne
Author: J. Kaastra
Author: C. Knigge
Author: K.T. Korista
Author: I. M. Mc Hardy
Author: R.W. Pogge
Author: D.A. Starkey
Author: M. Vestergaard

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