Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A Revised Limit of the Lorentz Factors of GRBs with Two Emitting Regions   Fermi observations of GeV emission from GRBs have suggested that the Lorentz
factor of some GRBs is around a thousand or even higher. At the same time the
same Fermi observations have shown an extended GeV emission indicating that
this higher energy emission might be a part of the afterglow and it does not
come from the same region as the lower energy prompt emission. If this
interpretation is correct than we should reconsider the opacity limits on the
Loretnz factor of the emitting regions which are based on a one-zone model. We
describe here a two-zone model in which the GeV photons are emitted in a larger
radius than the MeV photons and we calculate the optical depth for pair
creation of a GeV photon passing the lower energy photons shell. We find that,
as expected, the new two-zone limits on the Lorentz factor are significantly
lower. The corresponding limits for the Fermi bursts are lower by a factor of
five compared to the one-zone model and it is possible that both the MeV and
GeV regions have relatively modest Lorentz factors (~200 - 400).

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The categories of this paper are: alg-geom
3
The categories of this paper are: physics
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The categories of this paper are: adap-org
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The categories of this paper are: bayes-an
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The categories of this paper are: gr-qc
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The categories of this paper are: eess
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The categories of this paper are: mtrl-th
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The categories of this paper are: nlin
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The categories of this paper are: q-bio
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The categories of this paper are: hep-th
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The categories of this paper are: funct-an
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The categories of this paper are: solv-int
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The categories of this paper are: patt-sol
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The categories of this paper are: q-fin
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The categories of this paper are: atom-ph
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The categories of this paper are: plasm-ph