Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Gamma-ray bursts from internal shocks in a relativistic wind: temporal
  and spectral properties   We construct models for gamma-ray bursts where the emission comes from
internal shocks in a relativistic wind with a highly non uniform distribution
of the Lorentz factor. We follow the evolution of the wind using a very
simplified approach where a large number of layers interact by direct
collisions but where all pressure waves have been suppressed. We suppose that
the magnetic field and the electron Lorentz factor reach large equipartition
values in the shocks. Synchrotron photons emitted by the relativistic electrons
have a typical energy in the gamma-ray range in the observer frame. Synthetic
bursts are constructed as the sum of the contributions from all the internal
elementary shocks and their temporal and spectral properties are compared to
the observations. We reproduce the diversity of burst profiles, the ``FRED''
shape of individual pulses and the short time scale variability. Synthetic
bursts also satisfy the duration-hardness relation and individual pulses are
found to be narrower at high energy, in agreement with the observations. These
results suggest that internal shocks in a relativistic wind may indeed be at
the origin of gamma-ray bursts. A potential problem is however the relatively
low efficiency of the dissipation process. If the relativistic wind is powered
by accretion from a disc to a stellar mass black hole it implies that a
substantial fraction of the available energy is injected into the wind.

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The categories of this paper are: math
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The categories of this paper are: nucl-th
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The categories of this paper are: math-ph
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The categories of this paper are: stat
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The categories of this paper are: hep-ph
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The categories of this paper are: adap-org
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The categories of this paper are: plasm-ph
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The categories of this paper are: solv-int
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The categories of this paper are: nlin
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The categories of this paper are: mtrl-th
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The categories of this paper are: cmp-lg
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The categories of this paper are: comp-gas
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The categories of this paper are: cs
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The categories of this paper are: cond-mat
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The categories of this paper are: physics
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The categories of this paper are: funct-an