Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Asymmetry in the Outburst of SN 1987A Detected Using Light Echo
  Spectroscopy   We report direct evidence for asymmetry in the early phases of SN 1987A via
optical spectroscopy of five fields of its light echo system. The light echoes
allow the first few hundred days of the explosion to be reobserved, with
different position angles providing different viewing angles to the supernova.
Light echo spectroscopy therefore allows a direct spectroscopic comparison of
light originating from different regions of the photosphere during the early
phases of SN 1987A. Gemini multi-object spectroscopy of the light echo fields
shows fine-structure in the H-alpha line as a smooth function of position angle
on the near-circular light echo rings. H-alpha profiles originating from the
northern hemisphere of SN 1987A show an excess in redshifted emission and a
blue knee, while southern hemisphere profiles show an excess of blueshifted
H-alpha emission and a red knee. This fine-structure is reminiscent of the
"Bochum event" originally observed for SN 1987A, but in an exaggerated form.
Maximum deviation from symmetry in the H-alpha line is observed at position
angles 16 and 186 degrees, consistent with the major-axis of the expanding
elongated ejecta. The asymmetry signature observed in the H-alpha line smoothly
diminishes as a function of viewing angle away from the poles of the elongated
ejecta. We propose an asymmetric two-sided distribution of 56Ni most dominant
in the southern far quadrant of SN 1987A as the most probable explanation of
the observed light echo spectra. This is evidence that the asymmetry of
high-velocity 56Ni in the first few hundred days after explosion is correlated
to the geometry of the ejecta some 25 years later.

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The categories of this paper are: chem-ph
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The categories of this paper are: cmp-lg
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The categories of this paper are: stat
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The categories of this paper are: cond-mat
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The categories of this paper are: nucl-th
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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: bayes-an
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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: nlin
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The categories of this paper are: chao-dyn
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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: hep-ph
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The categories of this paper are: plasm-ph