Issue |
A&A
Volume 480, Number 2, March III 2008
|
|
---|---|---|
Page(s) | 305 - 312 | |
Section | Astrophysical processes | |
DOI | https://doi.org/10.1051/0004-6361:20079085 | |
Published online | 09 January 2008 |
Prompt GRB emission from gradual energy dissipation
Max Planck Institute for Astrophysics, Box 1317, 85741 Garching, Germany e-mail: giannios@mpa-garching.mpg.de
Received:
16
November
2007
Accepted:
24
December
2007
I calculate the emission expected from a Poynting-flux-dominated
gamma-ray burst (GRB) flow in which energy is dissipated gradually by
magnetic reconnection. In this picture, the energy of the radiating
particles is determined by heating and cooling balance (slow heating model).
Detailed radiative transfer calculations show that,
at Thomson optical depths of order of unity, the dominant radiative
process is inverse Compton scattering. Synchrotron-self-absorbed emission and inverse
Compton dominate in the Thomson thin parts of the flow.
The electrons stay thermal throughout the dissipation region
because of Coulomb collisions (Thomson thick part of the flow)
and exchange of synchrotron photons (Thomson thin part).
The resulting spectrum naturally explains the observed sub-MeV
break of the GRB emission and the spectral slopes above and below the break.
The model predicts that the γ-ray power-law tail has a high-energy
cutoff typically in the ~ GeV energy range that should be
observable with GLAST. The model also predicts a prompt emission
component in the optical and UV associated with the GeV emission.
Observations of the prompt emission of GRB 061121
that cover the energy range from the optical to ~1 MeV are explained by
the model.
Key words: gamma rays: bursts / radiation mechanisms: general / methods: statistical
© ESO, 2008
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