000004757 001__ 4757
000004757 005__ 20200203155420.0
000004757 0247_ $$2DOI$$a10.3847/1538-4357/ab1b48
000004757 037__ $$aSCART-2020-0057
000004757 100__ $$aDehghanian, M.
000004757 245__ $$aSpace Telescope and Optical Reverberation Mapping Project. X. Understanding the Absorption-line Holiday in NGC 5548
000004757 260__ $$c2019
000004757 520__ $$aThe Space Telescope and Optical Reverberation Mapping Project (AGN STORM) on NGC 5548 in 2014 is one of the most intensive multiwavelength AGN monitoring campaigns ever. For most of the campaign, the emission- line variations followed changes in the continuum with a time lag, as expected. However, the lines varied independently of the observed UV- optical continuum during a 60-70 day “holiday,” suggesting that unobserved changes to the ionizing continuum were present. To understand this remarkable phenomenon and to obtain an independent assessment of the ionizing continuum variations, we study the intrinsic absorption lines present in NGC 5548. We identify a novel cycle that reproduces the absorption line variability and thus identify the physics that allows the holiday to occur. In this cycle, variations in this obscurer’s line- of-sight covering factor modify the soft X-ray continuum, changing the ionization of helium. Ionizing radiation produced by recombining helium then affects the level of ionization of some ions seen by the Hubble Space Telescope. In particular, high-ionization species are affected by changes in the obscurer covering factor, which does not affect the optical or UV continuum, and thus appear as uncorrelated changes, a “holiday.” It is likely that any other model that selectively changes the soft X-ray part of the continuum during the holiday can also explain the anomalous emission-line behavior observed.
000004757 594__ $$aNO
000004757 6531_ $$agalaxies: active
000004757 6531_ $$agalaxies: individual: NGC 5548
000004757 6531_ $$agalaxies: nuclei
000004757 6531_ $$agalaxies: Seyfert
000004757 6531_ $$aline: formation
000004757 6531_ $$aAstrophysics - Astrophysics of Galaxies
000004757 700__ $$aFerland, G. J.
000004757 700__ $$aKriss, G. A.
000004757 700__ $$aPeterson, B. M.
000004757 700__ $$aMathur, S.
000004757 700__ $$aMehdipour, M.
000004757 700__ $$aGuzmán, F.
000004757 700__ $$aChatzikos, M.
000004757 700__ $$avan Hoof, P. A. M.
000004757 700__ $$aWilliams, R. J. R.
000004757 700__ $$aArav, N.
000004757 700__ $$aBarth, A. J.
000004757 700__ $$aBentz, M. C.
000004757 700__ $$aBisogni, S.
000004757 700__ $$aBrandt, W. N.
000004757 700__ $$aCrenshaw, D. M.
000004757 700__ $$aDalla Bontà, E.
000004757 700__ $$aDe Rosa, G.
000004757 700__ $$aFausnaugh, M. M.
000004757 700__ $$aGelbord, J. M.
000004757 700__ $$aGoad, M. R.
000004757 700__ $$aGupta, A.
000004757 700__ $$aHorne, Keith
000004757 700__ $$aKaastra, J.
000004757 700__ $$aKnigge, C.
000004757 700__ $$aKorista, K. T.
000004757 700__ $$aMcHardy, I. M.
000004757 700__ $$aPogge, R. W.
000004757 700__ $$aStarkey, D. A.
000004757 700__ $$aVestergaard, M.
000004757 773__ $$c119 (10 pages)$$n2$$pThe Astrophysical Journal$$v877$$y2019
000004757 8560_ $$fpeter.vanhoof@observatoire.be
000004757 85642 $$ahttps://arxiv.org/abs/1812.11578
000004757 905__ $$apublished in
000004757 980__ $$aREFERD