Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Spectral Variability and iron line emission in the ASCA Observations of
  the Seyfert 1 Galaxy NGC4051   We present the results of an extensive analysis of the ``ASCA'' AO2
observation of the Seyfert 1 galaxy NGC4051. The target exhibits broadband
[0.5--10 keV] variability by a factor $\sim 8$ on time scales $\sim 10^4 s$,
with a typical doubling time $\sim 500 s$. The spectrum is characterized by a
strong emission excess over the extrapolated power law at energies $E \le 1
keV$. Absorption edges due to ionized oxygen species OVII and OVIII are
detected together with an emission-like feature at $E \sim 0.93 keV$. The OVII
edge undergoes significant variability on a timescale as low as $\sim 10^4 s$,
whilst no contemporary variability of the OVIII feature is detected. Typical
variability time scales place constraints on the location and the density of
the absorbing matter. In the self-consistent hypothesis of a high energy ($E
\ge 2.3 keV$) power law reflected by an infinite plane-parallel cold slab, a
photon index change ($\Delta \Gamma = 0.4$) has also been observed; a natural
explanation can be found in the framework of non-thermal Comptonization models.
The iron line is redshifted (centroid energy $E \sim 6.1 keV$) and broad
($\sigma > 0.2 keV$); multicomponent structure is suggestive of emission from a
relativistic accretion disk; however if the disk is not ionized a contribution
by a molecular torus or an iron overabundance by a factor $\sim 1.5$ are
required.

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The categories of this paper are: physics
30
The categories of this paper are: q-alg
25
The categories of this paper are: patt-sol
18
The categories of this paper are: econ
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The categories of this paper are: quant-ph
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The categories of this paper are: cs
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The categories of this paper are: q-bio
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The categories of this paper are: nucl-ex
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The categories of this paper are: math
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The categories of this paper are: hep-lat
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The categories of this paper are: bayes-an
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The categories of this paper are: hep-ph
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The categories of this paper are: chem-ph
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The categories of this paper are: supr-con
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The categories of this paper are: atom-ph
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The categories of this paper are: cond-mat