Astronomy and Astrophysics – Astrophysics
Scientific paper
1994-04-18
Astrophys.J. 430 (1994) L93-L96
Astronomy and Astrophysics
Astrophysics
7 pages, plain TeX
Scientific paper
10.1086/187446
The 'event' that triggers a gamma ray burst cannot last for more than a few seconds. This is, however, long compared with the dynamical timescale of a compact stellar-mass object ($\sim 10^{-3}$ seconds). Energy is assumed to be released as an outflow with high mean lorentz factor $\Gamma$. But a compact stellar-mass collapse or merger is, realistically, likely to generate a mass (or energy) flux that is unsteady on some timescales in the range $10^{-3}$ - 10 seconds. If $\Gamma$ fluctuates by a factor of $\sim 2$ around its mean value, relative motions within the outflowing material will themselves (in the comoving frame) be relativistic, and can give rise to internal shocks. For $\Gamma \sim 10^2$, the resultant dissipation occurs outside the 'photosphere' and can convert a substantial fraction of the overall outflow energy into non-thermal radiation. This suggests a mechanism for cosmological bursts that demands less extreme assumptions (in respect of $\Gamma$-values, freedom from baryonic contamination, etc) than earlier proposals.
Meszaros Peter
Rees Martin J.
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