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Issue A&A Volume 391, Number 3, September I 2002 Page(s) 1141 - 1153 Section Physical and chemical processes DOI 10.1051/0004-6361:20020839

A&A 391, 1141-1153 (2002)
DOI: 10.1051/0004-6361:20020839

Efficient acceleration and radiation in Poynting flux powered GRB outflows

G. Drenkhahn and H. C. Spruit

Max-Planck-Institut für Astrophysik, Postfach 1317, 85741 Garching bei München, Germany

(Received 20 February 2002 / Accepted 4 June 2002 )

Abstract
We investigate the effects of magnetic energy release by local magnetic dissipation processes in Poynting flux-powered GRBs. For typical GRB parameters (energy and baryon loading) the dissipation takes place mainly outside the photosphere, producing non-thermal radiation. This process converts the total burst energy into prompt radiation at an efficiency of 10-50%. At the same time the dissipation has the effect of accelerating the flow to a large Lorentz factor. For higher baryon loading, the dissipation takes place mostly inside the photosphere, the efficiency of conversion of magnetic energy into radiation is lower, and an X-ray flash results instead of a GRB. We demonstrate these effects with numerical one-dimensional steady relativistic MHD calculations.

Key words: gamma rays: bursts -- magnetic fields -- magnetohydrodynamics (MHD) -- stars: winds, outflows

Offprint request: G. Drenkhahn, georg@mpa-garching.mpg.de

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