Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Distance Determination to the Crab-like PWN G54.1+0.3 and Search for its
  Supernova Remnant Shell   We discover a large-scale shell G53.9+0.2 around the Crab-like pulsar wind
nebula (PWN) G54.1+0.3 with 1420 MHz continuum VLA observations. This is
confirmed by a new infrared image at 8 \mu m from the GLIMPSE Legacy Project,
which reveals an intriguing infrared shell just surrounding the large radio
shell. We analyze the 21 cm HI absorption spectra and 13CO emission spectra
towards PWN G54.1+0.3 and bright sources on both radio and IR shells.
Continuous HI absorption up to the tangent point and absence of negative HI
absorption features imply that PWN G54.1+0.3 has a distance beyond the tangent
point but within the Solar circle, i.e. 4.5 to 9 kpc. G54.1+0.3 is likely at
distance of \simeq 6.2 kpc due to the morphological association between the PWN
and a CO molecular cloud at velocity of \simeq 53 km/s, as revealed by
high-resolution 13CO images. Based on the HI absorption spectrum and
recombination line velocity (\simeq 40 km/s) of the bright HII region
G54.09-0.06, which is on the IR shell, the IR shell is likely located at a
distance of \simeq 7.3 kpc, which is also the distance of the associated
large-scale radio shell. At this distance, the radio shell has a radius of ~ 30
pc. The radio shell may be thermal and lack IR emission due to dust
destruction, or it may be nonthermal and part of a newly found old SNR. In
either case it is located at a different distance than PWN G54.1+0.3.

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The categories of this paper are: acc-phys
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The categories of this paper are: ao-sci
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The categories of this paper are: quant-ph
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The categories of this paper are: eess
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The categories of this paper are: cs
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The categories of this paper are: q-bio
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The categories of this paper are: dg-ga
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The categories of this paper are: q-fin
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The categories of this paper are: nucl-ex
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The categories of this paper are: stat
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The categories of this paper are: atom-ph
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The categories of this paper are: solv-int
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The categories of this paper are: hep-ex
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The categories of this paper are: q-alg
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The categories of this paper are: cmp-lg
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The categories of this paper are: math-ph