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dc.contributor.authorDehghanian, M.
dc.contributor.authorFerland, G. J.
dc.contributor.authorKriss, G. A.
dc.contributor.authorPeterson, B. M.
dc.contributor.authorMathur, S.
dc.contributor.authorMehdipour, M.
dc.contributor.authorGuzmán, F.
dc.contributor.authorChatzikos, M.
dc.contributor.authorHoof, P. A. M. Van
dc.contributor.authorWilliams, R. J. R.
dc.contributor.authorArav, N.
dc.contributor.authorBarth, A. J.
dc.contributor.authorBentz, M. C.
dc.contributor.authorBisogni, S.
dc.contributor.authorBrandt, W. N.
dc.contributor.authorCrenshaw, D. M.
dc.contributor.authorDalla Bontà, E.
dc.contributor.authorDe Rosa, G.
dc.contributor.authorFausnaugh, M. M.
dc.contributor.authorGelbord, J. M.
dc.contributor.authorGoad, M. R.
dc.contributor.authorGupta, A.
dc.contributor.authorHorne, Keith
dc.contributor.authorKaastra, J.
dc.contributor.authorKnigge, C.
dc.contributor.authorKorista, K. T.
dc.contributor.authorMcHardy, I. M.
dc.contributor.authorPogge, R. W.
dc.contributor.authorStarkey, D. A.
dc.contributor.authorVestergaard, M.
dc.identifier.citationDehghanian , M , Ferland , G J , Kriss , G A , Peterson , B M , Mathur , S , Mehdipour , M , Guzmán , F , Chatzikos , M , Hoof , P A M V , Williams , R J R , Arav , N , Barth , A J , Bentz , M C , Bisogni , S , Brandt , W N , Crenshaw , D M , Dalla Bontà , E , De Rosa , G , Fausnaugh , M M , Gelbord , J M , Goad , M R , Gupta , A , Horne , K , Kaastra , J , Knigge , C , Korista , K T , McHardy , I M , Pogge , R W , Starkey , D A & Vestergaard , M 2019 , ' Space telescope and optical reverberation mapping project. X. Understanding the absorption-line holiday in NGC 5548 ' , Astrophysical Journal , vol. 877 , no. 2 , 119 .
dc.identifier.otherPURE: 259378588
dc.identifier.otherPURE UUID: d3dcc61b-a348-4e53-90d6-0e8efa31774f
dc.identifier.otherScopus: 85068958720
dc.identifier.otherWOS: 000470703700005
dc.descriptionFunding: UK STFC grant ST/R000824/1.en
dc.description.abstractThe Space Telescope and Optical Reverberation Mapping Project (AGN STORM) on NGC 5548 in 2014 is one of the most intensive multiwavelength AGN monitoring campaigns 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," suggesting that unobserved changes to the ionizing continuum were present. To understand this remarkable phenomenon and to obtain an independent assessment of the ionizing continuum variations, 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 this cycle, variations in this obscurer's line-of-sight covering factor modify the soft X-ray continuum, changing the ionization of helium. Ionizing radiation produced by recombining helium then affects the level of ionization of some ions seen by the Hubble Space Telescope. In particular, high-ionization species are affected by changes in the obscurer covering factor, which does not affect the optical or UV continuum, and thus appear as uncorrelated changes, a "holiday." It is likely that any other model that selectively changes the soft X-ray part of the continuum during the holiday can also explain the anomalous emission-line behavior observed.
dc.relation.ispartofAstrophysical Journalen
dc.rightsCopyright 2019 The American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.en
dc.subjectGalaxies: activeen
dc.subjectGalaxies: individual (NGC 5548)en
dc.subjectGalaxies: nucleien
dc.subjectGalaxies: Seyferten
dc.subjectLine: formationen
dc.subjectQB Astronomyen
dc.subjectQC Physicsen
dc.titleSpace telescope and optical reverberation mapping project. X. Understanding the absorption-line holiday in NGC 5548en
dc.typeJournal articleen
dc.description.versionPublisher PDFen
dc.contributor.institutionUniversity of St Andrews.School of Physics and Astronomyen
dc.contributor.institutionUniversity of St Andrews.St Andrews Centre for Exoplanet Scienceen
dc.description.statusPeer revieweden

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