Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A Possible Explanation for the Radio ``Flare'' in the Early Afterglow of
  GRB990123   We suggest that the deceleration of the relativistic shock by a denser part
of the interstellar medium off line-of-sight produced the observed radio
``flare'' in the early afterglow of GRB990123. We find that this scenario is
consistent with observations if the particle number density of this denser part
of the medium is between $\sim 200$ and $\sim 2\times 10^4$ cm$^{-3}$. Because
of the premature deceleration of part of the shock, the later stage of the
afterglow should decay modestly faster than the powerlaw expected from an
isotropic shock propagation.

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The categories of this paper are: econ
26
The categories of this paper are: bayes-an
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The categories of this paper are: q-fin
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The categories of this paper are: eess
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The categories of this paper are: gr-qc
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The categories of this paper are: dg-ga
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The categories of this paper are: funct-an
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The categories of this paper are: q-alg
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The categories of this paper are: hep-th
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The categories of this paper are: chem-ph
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The categories of this paper are: alg-geom
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The categories of this paper are: quant-ph
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The categories of this paper are: cmp-lg
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The categories of this paper are: solv-int
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The categories of this paper are: supr-con
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The categories of this paper are: nucl-th