Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A Chandra View of The Morphological And Spectral Evolution of Supernova
  Remnant 1987A   We present an update on the results of our monitoring observations of the
X-ray remnant of supernova (SN) 1987A with the {\it Chandra X-Ray Observatory}.
As of 2002 December, we have performed a total of seven observations of SN
1987A. The high angular resolution images from the latest data reveal
developments of new X-ray bright spots in the northwestern and the southwestern
portions of the remnant as well as changes on the eastern side. The latest
0.5-2 keV band flux ($f_X$ $\sim$ 6 $\times$ 10$^{-13}$ ergs cm$^{-2}$
s$^{-1}$) is four times brighter than three years earlier. The overall X-ray
emission is primarily from the blast wave shock with $kT$ $\sim$ 2.4 keV. As
the blast wave approaches the dense circumstellar material, the contribution
from the decelerated slow shock ($kT$ $\sim$ 0.22 keV) to the observed X-ray
emission is becoming significant. The increase of this slow shock contribution
over the last two years is particularly noticeable in the western half of the
remnant. These results indicate that the shock front is now reaching the main
body of the inner circumstellar ring. Based on the best-fit two-shock spectral
model, we derive approximate densities of the X-ray-emitting regions ($n_e$
$\sim$ 235 cm$^{-3}$ for the fast shock and $n_e$ $\sim$ 7500 cm$^{-3}$ for the
slow shock). We obtain an upper limit on the observed X-ray luminosity of any
embedded point source ($L_X$ $\le$ 1.5 $\times$ 10$^{34}$ ergs s$^{-1}$) in the
2$-$10 keV band. The X-ray remnant continues to expand linearly at a rate of
4167 km s$^{-1}$.

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The categories of this paper are: eess
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The categories of this paper are: dg-ga
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The categories of this paper are: hep-ex
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The categories of this paper are: quant-ph
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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-fin
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The categories of this paper are: funct-an
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The categories of this paper are: hep-ph
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The categories of this paper are: chao-dyn
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The categories of this paper are: math
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The categories of this paper are: q-bio
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The categories of this paper are: chem-ph
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The categories of this paper are: atom-ph
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The categories of this paper are: mtrl-th
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The categories of this paper are: adap-org