Space telescope and optical reverberation mapping project. IV. Anomalous behavior of the broad ultraviolet emission lines in NGC 5548
- University of Leicester, Department of Physics and Astronomy, Leicester, LE1 7RH (United Kingdom)
- Department of Physics, Western Michigan University, 1120 Everett Tower, Kalamazoo, MI 49008-5252 (United States)
- Department of Astronomy, The Ohio State University, 140 West 18th Avenue, Columbus, OH 43210 (United States)
- Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218 (United States)
- Department of Astronomy, University of Maryland, College Park, MD 20742-2421 (United States)
- Department of Physics and Astronomy, 4129 Frederick Reines Hall, University of California, Irvine, CA 92697 (United States)
- Department of Physics and Astronomy, The University of Kentucky, Lexington, KY 40506 (United States)
- School of Physics and Astronomy, Raymond and Beverly Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978 (Israel)
- Department of Physics and Astronomy, Georgia State University, 25 Park Place, Suite 605, Atlanta, GA 30303 (United States)
- Department of Astronomy and Astrophysics, Eberly College of Science, The Pennsylvania State University, 525 Davey Laboratory, University Park, PA 16802 (United States)
- SUPA Physics and Astronomy, University of St. Andrews, Fife, KY16 9SS Scotland (United Kingdom)
- SRON Netherlands Institute for Space Research, Sorbonnelaan 2, 3584 CA Utrecht (Netherlands)
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 ∼60–70 days, starting ∼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 Lyα was substantially smaller. This pattern of behavior indicates a depletion in the flux of photons with E{sub 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.
- OSTI ID:
- 22868836
- Journal Information:
- Astrophysical Journal, Vol. 824, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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