Space Telescope and Optical Reverberation Mapping Project. X. Understanding the Absorption-line Holiday in NGC 5548
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Author
Dehghanian, M.Ferland, G. J.

Kriss, G. A.
Peterson, B. M.
Mathur, S.
Mehdipour, M.
Guzmán, 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.
Bontà, E. Dalla
De Rosa, G.
Fausnaugh, M. M.
Gelbord, J. M.
Goad, M. R.
Gupta, A.
Horne, Keith
Kaastra, J.
Knigge, C.
Korista, K. T.
McHardy, I. M.
Pogge, R. W.

Starkey, D. A.
Vestergaard, M.
Affiliation
Univ Arizona, Steward ObservIssue Date
2019-06-03Keywords
galaxies: activegalaxies: individual (NGC 5548)
galaxies: nuclei
galaxies: Seyfert
line: formation
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IOP PUBLISHING LTDCitation
M. Dehghanian et al 2019 ApJ 877 119Journal
ASTROPHYSICAL JOURNALRights
Copyright © 2019. The American Astronomical Society. All rights reserved.Collection Information
This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at repository@u.library.arizona.edu.Abstract
The 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.ISSN
0004-637XVersion
Final published versionSponsors
NASA through a grant from the Space Telescope Science Institute [NNX15AH49G, 80NSSC17K0126, NAS5-26555]; NSF [1816537, AST-1816537, AST-1412693, AST-1009756, AST-1412315]; NASA [NNX15AH49G, 80NSSC17K0126, ATP 17-0141, AR7-18013X, NAS8-03060, PF5-160141]; STScI [HST-AR.13914, HST-AR-15018]; NASA through STScI grant [HST-AR-14556.001A, HST-AR-14286]; Huffaker Scholarship; National Science Foundation [AST-1008882]; NSF CAREER [AST-1253702]; Padua University [DOR1699945/16, DOR1715817/17, DOR1885254/18, BIRD164402/16]; NSF Fellowship award [AST-1302093]; STFC [ST/R000824/1, ST/M001326/1]; NWO; Netherlands Organization for Scientific Research; Packard Foundation; Danish Council [DFF 4002-00275]; Royal Society Leverhulme Trust Senior Research Fellowship [LT160006]; [HST-AR-13240.009]ae974a485f413a2113503eed53cd6c53
10.3847/1538-4357/ab1b48