Journal
ASTROPHYSICAL JOURNAL
Volume 824, Issue 1, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.3847/0004-637X/824/1/11
Keywords
galaxies: active; galaxies: individual (NGC-5548); galaxies: nuclei; galaxies: Seyfert
Categories
Funding
- NASA through Space Telescope Science Institute [GO-13330]
- NASA [NAS5-26555, NNX13AC26G, NNX13AC63G, NNX13AE99G, NNH13CH61C]
- National Science Foundation (NSF) [AST-1008882]
- NSF [AST-1412693, AST-1211916, AST-1302093, AST0618209, AST-1009756, AST-1009571, AST-1210311, AST-1412315]
- TABASGO Foundation
- Christopher R. Redlich Fund
- NSF CAREER grant [AST-1253702]
- NSERC
- UK Science and Technology Facilities Council [ST/J001651/1]
- Creative Initiative program of the National Research Foundation of Korea (NRFK) - Korean government (MSIP) [2008-0060544]
- NWO, the Netherlands Organization for Scientific Research
- UC Center for Galaxy Evolution
- Fondecyt [1120328]
- UCSB
- CNPq, National Council for Scientific and Technological Development (Brazil)
- Packard Foundation
- Danish National Research Foundation
- Danish Council for Independent Research [DFF4002-00275]
- National Research Foundation of Korea (NRF) - Korean government [2010-0027910]
- HHMI
- STFC [ST/N000757/1, ST/J001651/1, ST/N000811/1, ST/K001000/1] Funding Source: UKRI
- Science and Technology Facilities Council [1443664, ST/J001651/1] Funding Source: researchfish
- UK Space Agency [ST/P002196/1] Funding Source: researchfish
- Division Of Astronomical Sciences
- Direct For Mathematical & Physical Scien [1412155, 1302093, 1412315] Funding Source: National Science Foundation
- Division Of Astronomical Sciences
- Direct For Mathematical & Physical Scien [1253702, 1412693, 1008882, 1210311] Funding Source: National Science Foundation
- National Research Foundation of Korea [2010-0027910] Funding Source: Korea Institute of Science & Technology Information (KISTI), National Science & Technology Information Service (NTIS)
- NASA [NNX13AC26G, 476516, NNX13AC63G, 475364, NNX13AE99G, 476413] Funding Source: Federal RePORTER
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During an intensive Hubble Space Telescope (HST) Cosmic Origins Spectrograph (COS) UV monitoring campaign of the Seyfert 1 galaxy NGC 5548 performed from 2014 February to July, the normally highly correlated far UV continuum and broad emission line variations decorrelated for similar to 60-70 days, starting similar to 75 days after the first HST/COS observation. Following this anomalous state, the flux and variability of the broad emission lines returned to a more normal state. This transient behavior, characterized by significant deficits in flux and equivalent width of the strong broad UV emission lines, is the first of its kind to be unambiguously identified in an active galactic nucleus reverberation mapping campaign. The largest corresponding emission line flux deficits occurred for the high ionization, collisionally excited lines C IV and Si IV(+O IV]), and also He II(+O III]), while the anomaly in Ly alpha was substantially smaller. This pattern of behavior indicates a depletion in the flux of photons with E-ph > 54 eV relative to those near 13.6 eV. We suggest two plausible mechanisms for the observed behavior: (i) temporary obscuration of the ionizing continuum incident upon broad line region (BLR) clouds by a moving veil of material lying between the inner accretion disk and inner (BLR), perhaps resulting from an episodic ejection of material from the disk, or (ii) a temporary change in the intrinsic ionizing continuum spectral energy distribution resulting in a deficit of ionizing photons with energies > 54 eV, possibly due to a transient restructuring of the Comptonizing atmosphere above the disk. Current evidence appears to favor the latter explanation.
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