Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Evolution of the Accretion Disk around 4U 1820-30 During a
  Superburst   Accretion from a disk onto a collapsed, relativistic star -- a neutron star
or black hole -- is the mechanism widely believed to be responsible for the
emission from compact X-ray binaries. Because of the extreme spatial resolution
required, it is not yet possible to directly observe the evolution or dynamics
of the inner parts of the accretion disk where general relativistic effects are
dominant. Here, we use the bright X-ray emission from a superburst on the
surface of the neutron star 4U 1820-30 as a spotlight to illuminate the disk
surface. The X-rays cause iron atoms in the disk to fluoresce, allowing a
determination of the ionization state, covering factor and inner radius of the
disk over the course of the burst. The time-resolved spectral fitting shows
that the inner region of the disk is disrupted by the burst, possibly being
heated into a thicker, more tenuous flow, before recovering its previous form
in ~1000 s. This marks the first instance that the evolution of the inner
regions of an accretion disk has been observed in real-time.

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The categories of this paper are: nlin
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The categories of this paper are: physics
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The categories of this paper are: chao-dyn
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The categories of this paper are: patt-sol
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The categories of this paper are: cs
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The categories of this paper are: hep-ex
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The categories of this paper are: atom-ph
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The categories of this paper are: funct-an
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The categories of this paper are: hep-th
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The categories of this paper are: bayes-an
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The categories of this paper are: ao-sci
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The categories of this paper are: comp-gas
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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: math
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The categories of this paper are: econ