Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A New X-Ray Flare from the Galactic Nucleus Detected with the XMM-Newton
  Photon Imaging Cameras   Sgr A*, the compact radio source, believed to be the counterpart of the
massive black hole at the galactic nucleus, was observed to undergo rapid and
intense flaring activity in X-rays with Chandra in October 2000. We report here
the detection with XMM-Newton EPIC cameras of the early phase of a similar
X-ray flare from this source, which occurred on September 4, 2001. The source
2-10 keV luminosity increased by a factor about 20 to reach a level of 4
10^{34} erg s^{-1} in a time interval of about 900 s, just before the end of
the observation. The data indicate that the source spectrum was hard during the
flare. This XMM-Newton observation confirms the results obtained by Chandra and
suggests that, in Sgr A*, rapid and intense X-ray flaring is not a rare event.
This can constrain the emission mechanism models proposed for this source, and
also implies that the crucial multiwavelength observation programs planned to
explore the behaviour of the radio/sub-mm and hard X-ray/gamma-ray emissions
during the X-ray flares, have a good chance of success.

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The categories of this paper are: patt-sol
10
The categories of this paper are: q-bio
35
The categories of this paper are: mtrl-th
3
The categories of this paper are: physics
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The categories of this paper are: hep-lat
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The categories of this paper are: stat
5
The categories of this paper are: gr-qc
0
The categories of this paper are: hep-ph
32
The categories of this paper are: atom-ph
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The categories of this paper are: adap-org
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The categories of this paper are: solv-int
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The categories of this paper are: cmp-lg
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The categories of this paper are: comp-gas
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The categories of this paper are: eess
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The categories of this paper are: nlin
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The categories of this paper are: econ