Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: An Update on the X-ray transient Narrow-Line Seyfert 1 galaxy WPVS 007:
  Swift observations of UV variability and persistence of X-ray faintness   We report on the detection of UV variability and the persistence of X-ray
faintness of the X-ray transient Narrow-Line Seyfert 1 galaxy WPVS 007 based on
the first year of monitoring this AGN with Swift between 2005 October and 2007
January. WPVS 007 has been an unusual source. While being X-ray bright during
the ROSAT All-Sky Survey it has been extremely faint in all following X-ray
observations. Swift also finds this NLS1 to be X-ray faint and not detected in
the Swift X-Ray Telescope at an 3$\sigma$ upper limit of $2.6\times 10^{-17}$ W
m$^{-2}$ in the 0.3-10.0 keV band and confirms that the AGN is still in a low
state. During the 2006 July and December observations with \swift's UV-Optical
Telescope (UVOT) the AGN became fainter by about 0.2 mag in the UV filters and
by about 0.1 mag in V, B, and U compared with the 2005 October to 2006 January
and 2006 September/October observations followed by a rebrightening in the 2007
January observation. This variability can be caused either by a change in the
absorption column density and therefore the reddening in the UV, or by flux
variations of the central engine. We also noticed that the flux in the UVOT
filters agree with earlier measurements by the International Ultraviolet
Explorer taken between 1993-1995, but spectra taken by the Hubble Space
Telescope Faint Object Spectrograph show that WPVS 007 was fainter in the UV by
a factor of at least 2 in 1996. The flat optical/UV spectrum suggests that some
UV extinction is present in the spectrum, but that alone cannot at all account
for the dramatic fading in the X-ray flux. Most likely we see a partial
covering absorber in X-rays. Alternatively, the current X-ray emission seen
from WPVS 007 may also be the emission from the host galaxy.

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The categories of this paper are: cs
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The categories of this paper are: comp-gas
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The categories of this paper are: ao-sci
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The categories of this paper are: gr-qc
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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: plasm-ph
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The categories of this paper are: cond-mat
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The categories of this paper are: quant-ph
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The categories of this paper are: nucl-th
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The categories of this paper are: hep-th
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The categories of this paper are: adap-org
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The categories of this paper are: q-fin
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The categories of this paper are: acc-phys
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The categories of this paper are: q-bio
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The categories of this paper are: funct-an