Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A High-Velocity Scatterer Revealed in the Thinning Ejecta of a Type II
  Supernova   We present deep, nebular-phase spectropolarimetry of the Type II-P/L SN
2013ej, obtained 167 days after explosion with the European Southern
Observatory's Very Large Telescope. The polarized flux spectrum appears as a
nearly perfect (92% correlation), redshifted (by ~4,000 km/sec) replica of the
total flux spectrum. Such a striking correspondence has never been observed
before in nebular-phase supernova spectropolarimetry, although data capable of
revealing it have heretofore been only rarely obtained. Through comparison with
2D polarized radiative transfer simulations of stellar explosions, we
demonstrate that localized ionization produced by the decay of a high-velocity,
spatially confined clump of radioactive 56-Ni -- synthesized by and launched as
part of the explosion with final radial velocity exceeding 4,500 km/sec -- can
reproduce the observations through enhanced electron scattering. Additional
data taken earlier in the nebular phase (day 134) yield a similarly strong
correlation (84%) and redshift, whereas photospheric-phase epochs that sample
days 8 through 97, do not. This suggests that the primary polarization
signatures of the high-velocity scattering source only come to dominate once
the thick, initially opaque hydrogen envelope has turned sufficiently
transparent. This detection in an otherwise fairly typical core-collapse
supernova adds to the growing body of evidence supporting strong asymmetries
across Nature's most common types of stellar explosions, and establishes the
power of polarized flux -- and the specific information encoded by it in line
photons at nebular epochs -- as a vital tool in such investigations going
forward.

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The categories of this paper are: nlin
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The categories of this paper are: nucl-th
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The categories of this paper are: solv-int
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The categories of this paper are: math
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The categories of this paper are: physics
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The categories of this paper are: dg-ga
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The categories of this paper are: bayes-an
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The categories of this paper are: eess
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The categories of this paper are: hep-th
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The categories of this paper are: acc-phys
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The categories of this paper are: mtrl-th
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The categories of this paper are: patt-sol
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The categories of this paper are: supr-con
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The categories of this paper are: math-ph
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The categories of this paper are: ao-sci
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The categories of this paper are: stat