Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: X-ray Evolution of SNR 1987A: The Radial Expansion   We present the evolution of the radial expansion of SNR 1987A as measured
using Chandra X-ray observations taken over the last 10 years. To characterize
the complex structure of the remnant and isolate the expansion measurement, we
fit the images to several empirical models including: a simple circular torus,
a torus with bilateral lobes, and a torus with four tangentially extended
lobes. We discuss the results of this measure in the context of the overall
evolution of the supernova remnant, for which we believe we have measured the
end of the free expansion phase and its transition to the adiabatic phase (at
least along the equatorial ring). The timing of this event is in agreement with
early predictions of the remnant evolution.

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The categories of this paper are: math-ph
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The categories of this paper are: cmp-lg
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The categories of this paper are: atom-ph
5
The categories of this paper are: gr-qc
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The categories of this paper are: solv-int
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The categories of this paper are: comp-gas
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The categories of this paper are: adap-org
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The categories of this paper are: hep-th
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The categories of this paper are: funct-an
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The categories of this paper are: nlin
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The categories of this paper are: chem-ph
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The categories of this paper are: quant-ph
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The categories of this paper are: hep-ex
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The categories of this paper are: bayes-an
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The categories of this paper are: nucl-th
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The categories of this paper are: q-alg