Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: FIRST `Winged' and `X'-shaped Radio Source Candidates   A small number of double-lobed radio galaxies are found with an additional
pair of extended low surface brightness `wings' of emission giving them a
distinctive `X'-shaped appearance. One popular explanation for the unusual
morphologies posits that the central supermassive black hole (SMBH)/accretion
disk system underwent a recent realignment; in a merger scenario, the active
lobes mark the post-merger axis of the resultant system. However, this and
other interpretations are not well tested on the few (about one dozen) known
examples. In part to remedy this deficiency, a large sample of winged and
X-shaped radio sources is being compiled for a systematic study. An initial
sample of 100 new candidates is described as well as some of the follow-up work
being pursued to test the different scenarios.

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The categories of this paper are: mtrl-th
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The categories of this paper are: ao-sci
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The categories of this paper are: chem-ph
3
The categories of this paper are: physics
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The categories of this paper are: econ
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The categories of this paper are: funct-an
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The categories of this paper are: nucl-th
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The categories of this paper are: q-bio
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The categories of this paper are: gr-qc
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The categories of this paper are: plasm-ph
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The categories of this paper are: eess
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The categories of this paper are: math-ph
2
The categories of this paper are: math
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The categories of this paper are: comp-gas
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The categories of this paper are: bayes-an
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The categories of this paper are: dg-ga