Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Steps Toward Determination of the Size and Structure of the Broad-Line
  Region in Active Galactic Nuclei. XV. Long-Term Optical Monitoring of NGC
  5548   We present the results of three years of ground-based observations of the
Seyfert 1 galaxy NGC 5548, which combined with previously reported data, yield
optical continuum and broad-line H-beta light curves for a total of eight
years. The light curves consist of over 800 points, with a typical spacing of a
few days between observations. During this eight-year period, the nuclear
continuum has varied by more than a factor of seven, and the H-beta emission
line has varied by a factor of nearly six. The H-beta emission line responds to
continuum variations with a time delay or lag of 10-20 days, the precise value
varying somewhat from year to year. We find some indications that the lag
varies with continuum flux in the sense that the lag is larger when the source
is brighter.

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The categories of this paper are: q-fin
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The categories of this paper are: cmp-lg
31
The categories of this paper are: ao-sci
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The categories of this paper are: chao-dyn
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The categories of this paper are: acc-phys
2
The categories of this paper are: math
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The categories of this paper are: dg-ga
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The categories of this paper are: alg-geom
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The categories of this paper are: hep-th
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The categories of this paper are: comp-gas
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The categories of this paper are: cond-mat
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The categories of this paper are: hep-ex
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The categories of this paper are: solv-int
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The categories of this paper are: bayes-an
0
The categories of this paper are: hep-ph
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The categories of this paper are: stat