Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Comment on "Gamma-ray burst early afterglows: reverse shock emission
  from an arbitrarily magnetized ejecta" by Zhang and Kobayashi (2004)   Zhang and Kobayashi (2004) attempted to calculate early afterglow emission
from a system of forward and reverse shocks in GRB outflows for the case of
magnetized ejecta. We point out a fundamental error in the underlying dynamical
model. According to the authors, energy and momentum carried by the magnetic
field of the ejecta are not transfered to the forward shock. This is an
incorrect assumption that invalidates the results.

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The categories of this paper are: q-alg
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The categories of this paper are: math
11
The categories of this paper are: hep-lat
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The categories of this paper are: ao-sci
26
The categories of this paper are: bayes-an
9
The categories of this paper are: nlin
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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: supr-con
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The categories of this paper are: quant-ph
4
The categories of this paper are: cond-mat
7
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: physics
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The categories of this paper are: eess
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The categories of this paper are: stat