Spectra of Poynting-flux powered GRB outflows
Max Planck Institute for Astrophysics, Box 1317, 85741 Garching, Germany e-mail: email@example.com
2 University of Crete, Physics Department, PO Box 2208, 710 03 Heraklion, Crete, Greece
3 Foundation for Research and Technology-Hellas, 711 10 Heraklion, Crete, Greece
Accepted: 25 August 2004
We investigate the production of the gamma-ray spectrum of a Poynting-flux dominated GRB outflow. The very high magnetic field strengths (super-equipartition) in such a flow lead to very efficient synchrotron emission. In contrast with internal shocks, dissipation of magnetic energy by reconnection is gradual and does not produce the spectrum of cooling electrons associated with shock acceleration. We show that a spectrum with a break in the BATSE energy range is produced, instead, if the magnetic dissipation heats a small (~10-4) population of electrons.
Key words: gamma rays: bursts / magnetohydrodynamics (MHD) / radiation mechanisms: non-thermal
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