Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Precursors and Main-bursts of Gamma Ray Bursts in a Hypernova Scenario   We investigate a "hypernova" model for gamma-ray bursts (GRBs), i.e., massive
C+O star model with relativistic jets. In this model, non-thermal precursors
can be produced by the "first" relativistic shell ejected from the star. Main
GRBs are produced behind the "first"-shell by the collisions of several
relativistic shells. They become visible to distant observers after the
colliding region becomes optically thin. We examine six selected conditions
using relativistic hydrodynamical simulations and simple analyses.
Interestingly, our simulations show that sub-relativistic $(v \sim 0.8c)$ jets
from the central engine is sufficient to produce highly-relativistic $(\Gamma >
100)$ shells. We find that the relativistic shells from such a star can
reproduce observed GRBs with certain conditions. Two conditions are especially
important. One is the sufficiently long duration of the central engine $ \gsim
100$ sec. The other is the existence of a dense-shell somewhere behind the
"first"-shell. Under these conditions, both the existence and non-existence of
precursors, and long delay between precursors and main GRBs can be explained.

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The categories of this paper are: nucl-ex
37
The categories of this paper are: supr-con
3
The categories of this paper are: physics
21
The categories of this paper are: adap-org
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The categories of this paper are: nucl-th
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The categories of this paper are: quant-ph
0
The categories of this paper are: hep-ph
1
The categories of this paper are: cs
7
The categories of this paper are: hep-th
9
The categories of this paper are: nlin
26
The categories of this paper are: bayes-an
30
The categories of this paper are: q-alg
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The categories of this paper are: eess
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The categories of this paper are: stat
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The categories of this paper are: econ
4
The categories of this paper are: cond-mat