Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Fading of Supernova Remnant Cassiopeia A from 38 MHz to 16.5 GHz
  from 1949 to 1999 with New Observations at 1405 MHz   We report 1405 MHz measurements of the flux density of the approximately 320
year old supernova remnant Cassiopeia A, relative to the flux density of Cygnus
A, made between 1995 and 1999. When compared to measurements made between 1957
and 1976, we find that the rate at which Cassiopeia A has been fading at this
and nearby frequencies has changed from approximately 0.9 % yr^-1 in the 1960s
to approximately 0.6 - 0.7 % yr^-1 now. Furthermore, we have collected from the
literature measurements of this fading rate at lower (38 - 300 MHz) and higher
(7.8 - 16.5 GHz) frequencies. We show that the fading rate has dropped by a
factor of approximately 3 over the past 50 years at the lower frequencies,
while remaining relatively constant at the higher frequencies, which is in
agreement with the findings of others. Our findings at 1405 MHz, in conjunction
with a measurement of the fading rate at the nearby frequency of 927 MHz by
Vinyajkin (1997), show an intermediate behavior at intermediate frequencies. We
also find that Cassiopeia A, as of approximately 1990, was fading at about the
same rate, approximately 0.6 - 0.7 % yr^-1, at all of these frequencies. Future
measurements are required to determine whether the fading rate will continue to
decrease at the lower frequencies, or whether Cassiopeia A will now fade at a
relatively constant rate at all of these frequencies.

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The categories of this paper are: ao-sci
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The categories of this paper are: adap-org
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The categories of this paper are: atom-ph
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The categories of this paper are: quant-ph
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The categories of this paper are: dg-ga
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The categories of this paper are: nucl-th
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The categories of this paper are: chao-dyn
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The categories of this paper are: gr-qc
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The categories of this paper are: funct-an
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The categories of this paper are: alg-geom
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The categories of this paper are: comp-gas
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The categories of this paper are: q-alg
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The categories of this paper are: acc-phys
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The categories of this paper are: q-fin
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The categories of this paper are: hep-ph
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The categories of this paper are: cmp-lg