Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A Multi-wavelength Study of the X-ray Sources in NGC 5018   The E3 giant elliptical galaxy NGC5018 was observed with the Chandra X-ray
Observatory on 14 April 2001. Results of analysis of these X-ray data as well
as of complementary optical, infrared, and radio data are reported. Seven X-ray
point sources, including the nucleus, were detected.If they are intrinsic to
NGC5018, then all six non-nuclear sources have luminosities exceeding E+39
ergs/s in the 0.5-8.0 keV energy band; placing them in the class of
Ultra-luminous X-ray sources. Comparison of X-ray source positions to archival
HST/WFPC2 images reveal four of the six non-nuclear sources are
spatially-coincident with bright, absolute-magnitude (V) around -8.6 mag,
objects. These four objects have optical magnitudes and (V-I) colors consistent
with globular clusters in NGC5018 but they also have X-ray-to-optical flux
ratios consistent with background active galactic nuclei. Strong, unpolarized,
radio emission has been detected from one of the optically-bright counterparts.
Another optically-bright counterpart was observed to vary by one mag in optical
observations taken 28 July 1997 and 04 Feb 1999. Extended X-ray emission is
detected within a 15"radius of the galaxy center at a luminosity of E+40 ergs/s
in the X-ray band. Its thermal X-ray spectrum (kT around 0.4 keV) and its
spatial coincidence with strong H_alpha emission are consistent with a hot gas
origin. The nucleus itself may be a weak X-ray source, around E+39 ergs/s, that
displays a radio spectrum typical of AGN.

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The categories of this paper are: math
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The categories of this paper are: physics
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The categories of this paper are: funct-an
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The categories of this paper are: cmp-lg
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The categories of this paper are: nlin
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The categories of this paper are: q-alg
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The categories of this paper are: cond-mat
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The categories of this paper are: cs
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The categories of this paper are: nucl-th
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The categories of this paper are: chem-ph
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The categories of this paper are: plasm-ph
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The categories of this paper are: q-fin
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The categories of this paper are: solv-int
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The categories of this paper are: math-ph
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The categories of this paper are: acc-phys
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The categories of this paper are: supr-con