Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: X-ray Evidence for Supermassive Black Holes at the Centers of Nearby
  Galaxies   We first present a short overview of X-ray probes of the black hole region of
active galaxies (AGN) and then concentrate on the X-ray search for supermassive
black holes (SMBHs) in optically non-active galaxies.
  The first part focuses on recent results from the X-ray observatories Chandra
and XMM-Newton which detected a wealth of new spectral features which originate
in the nuclear region of AGN.
  In the last few years, giant-amplitude, non-recurrent X-ray flares have been
observed from several non-active galaxies. All of them share similar
properties, namely: extreme X-ray softness in outburst, huge peak luminosity
(up to ~10^{44} erg/s), and the absence of optical signs of Seyfert activity.
Tidal disruption of a star by a supermassive black hole is the favored
explanation of these unusual events. The second part provides a review of the
initial X-ray observations, follow-up studies,and the relevant aspects of tidal
disruption models studied in the literature.

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The categories of this paper are: mtrl-th
19
The categories of this paper are: eess
17
The categories of this paper are: q-fin
10
The categories of this paper are: q-bio
0
The categories of this paper are: hep-ph
30
The categories of this paper are: q-alg
13
The categories of this paper are: quant-ph
31
The categories of this paper are: ao-sci
25
The categories of this paper are: patt-sol
32
The categories of this paper are: atom-ph
4
The categories of this paper are: cond-mat
29
The categories of this paper are: funct-an
11
The categories of this paper are: hep-lat
12
The categories of this paper are: nucl-th
8
The categories of this paper are: hep-ex
15
The categories of this paper are: nucl-ex