Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The nature of the outflow in gamma-ray bursts   The Swift satellite has enabled us to follow the evolution of gamma-ray burst
(GRB) fireballs from the prompt gamma-ray emission to the afterglow phase. The
early x-ray and optical data obtained by telescopes aboard the Swift satellite
show that the source for prompt gamma-ray emission, the emission that heralds
these bursts, is short lived and that its source is distinct from that of the
ensuing, long-lived afterglow. Using these data, we determine the distance of
the gamma-ray source from the center of the explosion. We find this distance to
be 1e15-1e16 cm for most bursts and we show that this is within a factor of ten
of the radius of the shock-heated circumstellar medium (CSM) producing the
x-ray photons. Furthermore, using the early gamma-ray, x-ray and optical data,
we show that the prompt gamma-ray emission cannot be produced in internal
shocks, nor can it be produced in the external shock; in a more general sense
gamma-ray generation mechanisms based on shock physics have problems explaining
the GRB data for the ten Swift bursts analyzed in this work. A magnetic field
dominated outflow model for GRBs has some attractive features, although the
evidence in its favor is inconclusive. Finally, the x-ray and optical data
allow us to provide an upper limit on the density of the CSM of about 10
protons per cubic cm at a distance of about 5e16 cm from the center of
explosion.

8
The categories of this paper are: hep-ex
5
The categories of this paper are: gr-qc
28
The categories of this paper are: alg-geom
24
The categories of this paper are: dg-ga
18
The categories of this paper are: econ
4
The categories of this paper are: cond-mat
21
The categories of this paper are: adap-org
33
The categories of this paper are: plasm-ph
0
The categories of this paper are: hep-ph
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The categories of this paper are: acc-phys
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The categories of this paper are: comp-gas
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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: funct-an
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The categories of this paper are: q-alg
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The categories of this paper are: stat