Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Positional Coincidence of H2O Maser and a Plasma Obscuring Torus in
  Radio Galaxy NGC 1052   We present multi-frequency simultaneous VLBA observations at 15, 22 and 43
GHz towards the nucleus of the nearby radio galaxy NGC 1052. These three
continuum images reveal a double-sided jet structure, whose relative intensity
ratios imply that the jet axis is oriented close to the sky plane. The steeply
rising spectra at 15-43 GHz at the inner edges of the jets strongly suggest
that synchrotron emission is absorbed by foreground thermal plasma. We detected
H2O maser emission in the velocity range of 1550-1850 km/s, which is redshifted
by 50-350 km/s with respect to the systemic velocity of NGC 1052. The
redshifted maser gas appears projected against both sides of the jet, in the
same manner as the HI seen in absorption. The H2O maser gas are located where
the free-free absorption opacity is large. This probably imply that the masers
in NGC 1052 are associated with a circumnuclear torus or disk as in the nucleus
of NGC 4258. Such circumnuclear structure can be the sence of accreting onto
the central engine.

27
The categories of this paper are: comp-gas
10
The categories of this paper are: q-bio
23
The categories of this paper are: solv-int
0
The categories of this paper are: hep-ph
26
The categories of this paper are: bayes-an
11
The categories of this paper are: hep-lat
33
The categories of this paper are: plasm-ph
37
The categories of this paper are: supr-con
31
The categories of this paper are: ao-sci
21
The categories of this paper are: adap-org
12
The categories of this paper are: nucl-th
14
The categories of this paper are: math-ph
16
The categories of this paper are: stat
36
The categories of this paper are: cmp-lg
35
The categories of this paper are: mtrl-th
24
The categories of this paper are: dg-ga