Résumé
The origin of the GRB prompt emission is a matter of open debate. The observed prompt spectra typically present a non-thermal component in the keV-MeV range, and possibly an additional thermal component at low energies. GRB spectra are usually reconstructed using phenomenological models, which adapt to the data with one or more components, such as the Band and the black-body functions. This work is rather based on numerical simulations of GRB prompt emission in internal shocks above the photosphere. The predicted spectra are well reproduced in the keV-MeV range by the four-parameter spectral function 'Internal Shock Synchrotron Model (ISSM)' proposed by Yassine et al. 2020. We perform time-integrated and time-resolved spectral analyses of the 460 most fluent bursts detected by Fermi-GBM in 10 years of observations. The ISSM spectral function significantly improves the goodness of the fits compared to the Band function, especially in time-integrated analysis. We compare the resulting distribution of the photon index below the peak energy with theoretical expectations in the internal shock scenario. Finally, using ISSM instead of Band to describe the non-thermal component of GRBs 100724B, 120323A and 131014A systematically reduces the significance of an additional thermal component, confirming that in this scenario the relativistic jet is initially magnetically dominated.