Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The X-ray Decay of the ultraluminous supernova SN 1978K in NGC 1313   The Type IIn supernova (SN) 1978K in the nearby galaxy NGC 1313 has remained
bright in multiwavelengths for more than $\sim 25$ yr. The archival data of SN
1978K collected with ROSAT, ASCA, XMM-Newton, and Chandra from 1990 to 2006
show no significant variation of the soft X-ray emission but a hint of flux
decrease in hard X-rays. In this work, we perform a detailed analysis using
more than 15 yr of XMM-Newton observations. Both the 0.5-2 keV and 2-10 keV
light-curves decline as $t^{-1}$ from 2000 to 2015. The transition of light
curve profiles can be explained in a way that the reverse shock was radiative
at an early phase and then became adiabatic at late times. Such a scenario is
also supported by the spectral analysis results. We also found a decrease in
the absorption column density, which indicates the presence of a cool shell
during the radiative phase.

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The categories of this paper are: alg-geom
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The categories of this paper are: atom-ph
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The categories of this paper are: ao-sci
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The categories of this paper are: eess
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The categories of this paper are: nucl-ex
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The categories of this paper are: cond-mat
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The categories of this paper are: plasm-ph
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The categories of this paper are: math
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The categories of this paper are: cmp-lg
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The categories of this paper are: dg-ga
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The categories of this paper are: q-bio
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The categories of this paper are: comp-gas
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The categories of this paper are: chem-ph
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The categories of this paper are: math-ph
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The categories of this paper are: hep-ph
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The categories of this paper are: q-alg