GRBs spectra in optically thick expanding plasma shells model

Details GRBs spectra in optically thick expanding plasma shells model GRBs spectra in optically thick expanding plasma shells model

Aug 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001icrc....7.2747a&link_type=abstract

Proceedings of the 27th International Cosmic Ray Conference. 07-15 August, 2001. Hamburg, Germany. Under the auspices of the Int

Physics

Scientific paper

We suppose that nonthermal spectra of radiation in the gamma-ray bursts (GRBs) are formed by optically thick spherical plasma shells that expand with relativistic velocities. The temperature of the shell decreases as power law. We discuss results of calculations which show that radiation spectrum of such shell is similar to observed spectra of GRBs. This model allows to define some characteristics of emitting regions. 1 Observed GRB spectra In spite of resent progress in the observations of x-ray, optical and radio counterparts of GRB the nature of their internal engine and mechanism of γ-ray emission still remains unclear. According BATSE observations GRB spectra are well described by Band model: NE(E), counts cm2 × s = A × Eα × e-E/E0 , E < E0 B × Eβ , E > E0 , (1) where α is low energy spectral index, β is high energy one. α, β, A B and E0 can be different for each GRB. The power law shape of this spectra can be possibly explained by a hypothesis of their nonthermal origin. Cohen and colegues (Cohen, 1997) found that the low energy spectral index α in the time-integrated spectra of GRBs is usially in the range -3 2 < α < 2 3 as predicted by synchrotron shock model (Tavani, 1996). However, in work (Crider, 1997) the time-resolved spectra of 99 GRBs were analysed and it was found that for these spectra the α index is often outside the limits of syncrotron shock model.

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