2004MNRAS.352L..35S -
Mon. Not. R. Astron. Soc., 352, L35-L39 (2004/August-2)
Gamma-ray bursts from synchrotron self-Compton emission.
STERN B.E. and POUTANEN J.
Abstract (from CDS):
The emission mechanism of gamma-ray bursts (GRBs) is still a matter of debate. The standard synchrotron energy spectrum of cooling electrons FE∝E–1/2 is much too soft to account for the majority of the observed spectral slopes. An alternative in the form of quasi-thermal Comptonization in a high-compactness source has difficulties in reproducing the peak of the observed photon distribution below a few hundred keV. We show here that for typical parameters expected in the GRB ejecta the observed spectra in the 20-1000 keV energy range can be produced by inverse Compton scattering of the synchrotron radiation in a partially self-absorbed regime. If the particles are continuously accelerated/heated over the lifetime of a source rather than being instantly injected, a prominent peak develops in their distribution at a Lorentz factor γ∼ 30-100, where synchrotron and inverse-Compton losses are balanced by acceleration and heating due to synchrotron self-absorption. The synchrotron peak should be observed at 10-100 eV, whereas the self-absorbed low-energy tail with FE∝E2 can produce the prompt optical emission (as in the case of GRB 990123). The first Compton scattering radiation by nearly monoenergetic electrons can then be as hard as FE∝E1, reproducing the hardness of most of the observed GRB spectra. The second Compton peak should be observed in the high-energy gamma-ray band, possibly being responsible for the 10-100 MeV emission detected in GRB 941017. A significant electron-positron pair production reduces the available energy per particle, moving the spectral peaks to lower energies as the burst progresses. The regime is very robust, operates in a broad range of parameter space and can explain most of the observed GRB spectra and their temporal evolution.
Abstract Copyright:
2004 RAS
Journal keyword(s):
radiation mechanisms: non-thermal - scattering - methods: numerical - gamma-rays: bursts - gamma-rays: theory
Simbad objects:
2
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