Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Space Telescope and Optical Reverberation Mapping Project. IV. Anomalous
  behavior of the broad ultraviolet emission lines in NGC 5548   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 to 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 Ly-alpha was substantially
smaller. This pattern of behavior indicates a depletion in the flux of photons
with E_{\rm 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 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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The categories of this paper are: plasm-ph
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The categories of this paper are: stat
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The categories of this paper are: cmp-lg
1
The categories of this paper are: cs
2
The categories of this paper are: math
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The categories of this paper are: q-fin
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The categories of this paper are: adap-org
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The categories of this paper are: alg-geom
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The categories of this paper are: hep-lat
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The categories of this paper are: eess
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The categories of this paper are: q-alg
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The categories of this paper are: quant-ph
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The categories of this paper are: funct-an
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The categories of this paper are: chem-ph
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The categories of this paper are: solv-int
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The categories of this paper are: dg-ga