Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Ultraluminous X-ray Source NGC 1313 X-2 (MS 0317.7-6647) and its
  Environment   We present new optical and {\it Chandra} observations of the field containing
the ultraluminous X-ray source NGC 1313 X-2. On an ESO 3.6 m image, the {\it
Chandra} error box embraces a $R=21.6$ point-like object and excludes a
previously proposed optical counterpart. The resulting X-ray/optical flux ratio
of NGC 1313 X-2 is $\sim 500$. The value of $f_X/f_{opt}$, the X-ray
variability history and the spectral distribution derived from a re-analysis of
the {\it ROSAT}, {\it ASCA} and {\it XMM} data indicate a luminous X-ray binary
in NGC 1313 as a likely explanation for NGC 1313 X-2. If the X-ray soft
component observed in the {\it XMM} EPIC spectrum originates from an accretion
disk, the inferred mass of the compact remnant is $\approx 100 M_\odot$, making
it an intermediate mass black hole. The derived optical luminosity ($L\approx
10^5 L_\odot$) is consistent with that of a $\approx 15-20 M_\odot$ companion.
The properties of the environment of NGC 1313 X-2 are briefly discussed.

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The categories of this paper are: hep-lat
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The categories of this paper are: econ
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The categories of this paper are: hep-ex
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The categories of this paper are: stat
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The categories of this paper are: eess
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The categories of this paper are: nucl-th
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The categories of this paper are: supr-con
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The categories of this paper are: plasm-ph
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The categories of this paper are: comp-gas
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The categories of this paper are: physics
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The categories of this paper are: cmp-lg
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The categories of this paper are: alg-geom
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The categories of this paper are: q-bio
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The categories of this paper are: chao-dyn
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The categories of this paper are: hep-ph
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The categories of this paper are: nucl-ex