Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Transmission- to reflection-dominated transition in Seyfert 2 galaxies:
  the XMM-Newton view   In this paper we present the current status of a XMM-Newton program to
observe an optically-defined, complete and unbiased sample of Compton-thick
Seyfert 2 galaxies. The main goal of this project is the measurement of the
occurrence rate of transition between transmission- (i.e.: Compton-thin), and
reflection-dominated spectral states. These transitions potentially provide
information on the distribution of the obscuring matter surrounding the
nucleus, and on the duty-cycle of the AGN activity. With about 2/3 of the whole
sample being observed, we detected 1 further transition out of 8 observed
objects, confirming previous suggestions that these transitions occur on
time-scales ~50-100 years.

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The categories of this paper are: hep-ph
30
The categories of this paper are: q-alg
10
The categories of this paper are: q-bio
14
The categories of this paper are: math-ph
28
The categories of this paper are: alg-geom
33
The categories of this paper are: plasm-ph
18
The categories of this paper are: econ
31
The categories of this paper are: ao-sci
34
The categories of this paper are: chem-ph
16
The categories of this paper are: stat
15
The categories of this paper are: nucl-ex
37
The categories of this paper are: supr-con
2
The categories of this paper are: math
26
The categories of this paper are: bayes-an
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The categories of this paper are: q-fin
35
The categories of this paper are: mtrl-th