posted on 2016-03-31, 14:26authored byM. R. Goad, K. T. Korista, G. De Rosa, G. A. Kriss, R. Edelson, A. J. Barth, G. J. Ferland, C. S. Kochanek, H. Netzer, B. M. Peterson, M. C. Bentz, S. G. Sergeev, M. Siegel, M. Spencer, H.-I. Sung, K. G. Teems, T. Treu, C. S. Turner, P. Uttley, C. Villfoth, Y. Weiss, J.-H. Woo, H. Yan, S. Young, W.-K. Zheng, S. Bisogni, D. M. Crenshaw, K. D. Denney, J. Ely, M. M. Fausnaugh, C. J. Grier, A. Gupta, K. D. Horne, J. Kaastra, A. Pancoast, L. Pei, R. W. Pogge, A. Skielboe, D. Starkey, M. Vestergaard, Y. Zu, M. D. Anderson, P. Arévalo, C. Bazhaw, G. A. Borman, T. A. Boroson, M. C. Bottorff, W. N. Brandt, A. A. Breeveld, B. J. Brewer, E. M. Cackett, M. T. Carini, K. V. Croxall, E. Dalla Bontà, A. De Lorenzo-Cáceres, M. Dietrich, N. V. Efimova, P. A. Evans, A. V. Filippenko, K. Flatland, N. Gehrels, S. Geier, J. M. Gelbord, L. Gonzalez, V. Gorjian, D. Grupe, P. B. Hall, S. Hicks, D. Horenstein, T. Hutchison, M. Im, J. J. Jensen, M. D. Joner, J. Jones, S. Kaspi, B. C. Kelly, J. A. Kennea, M. Kim, S. C. Kim, S. A. Klimanov, V. M. Larionov, J. C. Lee, D. C. Leonard, P. Lira, F. MacInnis, E. R. Manne-Nicholas, S. Mathur, I. M. McHardy, C. Montouri, R. Musso, S. V. Nazarov, R. P. Norris, J. A. Nousek, D. N. Okhmat, I. Papadakis, J. R. Parks, J.-U. Pott, S. E. Rafter, H.-W. Rix, D. A. Saylor, J. S. Schimoia, K. Schnülle
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,
characterised 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
Eph > 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 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
Funding
Support for HST program number GO-13330 was provided
by NASA 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. M.M.F.,
G.D.R., B.M.P., C.J.G., and R.W.P. are grateful for
the support of the National Science Foundation (NSF)
through grant AST-1008882 to The Ohio State University.
A.J.B. and L.P. have been supported by NSF grant
AST-1412693. A.V.F. and W.-K.Z. are grateful for fi-
nancial assistance from NSF grant AST-1211916, the
TABASGO Foundation, and the Christopher R. Redlich
Fund. M.C. Bentz gratefully acknowledges support
through NSF CAREER grant AST-1253702 to Georgia
State University. M.C. Bottorff acknowledges HHMI
for support through an undergraduate science education
grant to Southwestern University. K.D.D. is supported
by an NSF Fellowship awarded under grant AST-
1302093. R.E. gratefully acknowledges support from
NASA under awards NNX13AC26G, NNX13AC63G,
and NNX13AE99G. J.M.G. gratefully acknowledges support
from NASA under award NNH13CH61C. P.B.H.
is supported by NSERC. K.D.H. acknowledges support
from the UK Science and Technology Facilities Council
through grant ST/J001651/1. M.I. acknowledges support
from the Creative Initiative program, No. 2008-
0060544, of the National Research Foundation of Korea
(NRFK) funded by the Korean government (MSIP).
M.D.J. acknowledges NSF grant AST0618209. SRON is
financially supported by NWO, the Netherlands Organization
for Scientific Research. B.C.K. is partially supported
by the UC Center for Galaxy Evolution. C.S.K.
acknowledges the support of NSF grant AST-1009756.
D.C.L. acknowledges support from NSF grants AST-
1009571 and AST-1210311. P.L. acknowledges support
from Fondecyt grant #1120328. A.P. acknowledges support
from an NSF graduate fellowship and a UCSB
Dean’s Fellowship. J.S.S. acknowledges CNPq, National
Council for Scientific and Technologi
History
Citation
The Astrophysical Journal 824:11 (10pp), 2016 June 10
Author affiliation
/Organisation/COLLEGE OF SCIENCE AND ENGINEERING/Department of Physics and Astronomy