Astronomy and Astrophysics – Astrophysics
Scientific paper
2005-09-26
Astrophys.J.633:L17-L20,2005
Astronomy and Astrophysics
Astrophysics
8 pages, 2 figures. Accepted for publication in the Astrophysical Journal (Letters)
Scientific paper
10.1086/498136
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.
Maeda Kei--ichi
Nomoto Ken'ichi
Tominaga Nozomu
Umeda Hideyuki
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