Space Telescope and Optical Reverberation Mapping Project. X. Understanding the Absorption-line Holiday in NGC 5548

dc.contributor.authorDehghanian, M.en
dc.contributor.authorFerland, G. J.en
dc.contributor.authorKriss, G. A.en
dc.contributor.authorPeterson, B. M.en
dc.contributor.authorMathur, S.en
dc.contributor.authorMehdipour, M.en
dc.contributor.authorGuzman, F.en
dc.contributor.authorChatzikos, M.en
dc.contributor.authorvan Hoof, P. A. M.en
dc.contributor.authorWilliams, R. J. R.en
dc.contributor.authorArav, Nahumen
dc.contributor.authorBarth, A. J.en
dc.contributor.authorBentz, M. C.en
dc.contributor.authorBisogni, S.en
dc.contributor.authorBrandt, W. N.en
dc.contributor.authorCrenshaw, D. M.en
dc.contributor.authorDalla Bonta, E.en
dc.contributor.authorDe Rosa, G.en
dc.contributor.authorFausnaugh, M. M.en
dc.contributor.authorGelbord, J. M.en
dc.contributor.authorGoad, M. R.en
dc.contributor.authorGupta, A.en
dc.contributor.authorHorne, Keithen
dc.contributor.authorKaastra, J.en
dc.contributor.authorKnigge, C.en
dc.contributor.authorKorista, K. T.en
dc.contributor.authorMcHardy, I. M.en
dc.contributor.authorPogge, R. W.en
dc.contributor.authorStarkey, D. A.en
dc.contributor.authorVestergaard, M.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.en
dc.description.notesNASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. We thank NSF (1816537), NASA (ATP 17-0141), and STScI (HST-AR.13914, HST-AR-15018) for their support and Huffaker scholarship for funding the trip to Atlanta to attend the annual AGN STORM meeting, 2017. M.C. acknowledges support from NASA through STScI grant HST-AR-14556.001A and STScI grant HST-AR-14286. M.D., G.F., and F.G. acknowledge support from the NSF (AST-1816537), NASA (ATP 17-0141), and STScI (HST-AR-13914, HST-AR-15018), and the Huffaker Scholarship. B.M.P., G.D.R., M.M.F,C.J.G., and R.W.P. are grateful for the support of the National Science Foundation through grant AST-1008882 to The Ohio State University. A.J.B. has been supported by NSF grant AST-1412693. M.C. B. gratefully acknowledges support through NSF CAREER grant AST-1253702 to Georgia State University. S.B. is supported by NASA through the Chandra award no. AR7-18013X issued by the Chandra X-ray Observatory Center, operated by the Smithsonian Astrophysical Observatory for and on behalf of NASA under contract NAS8-03060. S. B. was also partially supported by grant HST-AR-13240.009. E.D.B. acknowledge support from Padua University through grants DOR1699945/16, DOR1715817/17, DOR1885254/18, and BIRD164402/16. K.D.D. is supported by an NSF Fellowship awarded under grant AST-1302093. R. E. gratefully acknowledges support from NASA under the ADAP award 80NSSC17K0126. K.H. acknowledges support from STFC grant ST/R000824/1. SRON is financially supported by NWO, the Netherlands Organization for Scientific Research. C. S. K. acknowledges the support of NSF grant AST-1009756. A.P. is supported by NASA through Einstein Postdoctoral Fellowship grant number PF5-160141 awarded by the Chandra X-ray Center, which is operated by the Smithsonian Astrophysical Observatory for NASA under contract NAS8-03060. T. T. has been supported by NSF grant AST-1412315. T. T. and B. C. K. acknowledge support from the Packard Foundation in the form of a Packard Research Fellowship to T. T. The American Academy in Rome and the Observatory of Monteporzio Catone are thanked by T. T. for kind hospitality. M. V. gratefully acknowledges support from the Danish Council for Independent Research via grant No. DFF 4002-00275. This research has made use of the NASA/IPAC Extragalactic Database (NED), which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. I. McH. acknowledges support from a Royal Society Leverhulme Trust Senior Research Fellowship LT160006 and from STFC grant ST/M001326/1. J.M.G. gratefully acknowledges support from NASA under awards NNX15AH49G and 80NSSC17K0126. E.D.B. acknowledges support from Padua University through grants DOR1699945/16, DOR1715817/17, and DOR1885254/18.en
dc.description.sponsorshipNASA 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]en
dc.rightsCreative Commons Attribution 3.0 Unporteden
dc.subjectgalaxies: activeen
dc.subjectgalaxies: individual (NGC 5548)en
dc.subjectgalaxies: nucleien
dc.subjectgalaxies: Seyferten
dc.subjectline: formationen
dc.titleSpace Telescope and Optical Reverberation Mapping Project. X. Understanding the Absorption-line Holiday in NGC 5548en
dc.title.serialAstrophysical Journalen
dc.typeArticle - Refereeden


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