Description
The radiation mechanism of the prompt emission is still an open issue and can be resolved using a systematic and uniform time-resolved spectro-polarimetric study. In this work, we performed a comprehensive investigation of the spectral, temporal, and polarimetric characteristics of bright GRBs observed using the AstroSat CZTI, Fermi GBM, and Swift-BAT to provide insight into the prompt emission radiation mechanisms. We investigated the time-resolved (in 100-600 keV) and energy-resolved polarization measurements of these GRBs with an improved polarimetric technique. In addition, we also carried out detailed time-resolved spectral analyses of these GRBs using empirical and physical synchrotron models. By these improved time-resolved and energy-resolved spectro-polarimetric studies, we could pin down the elusive prompt emission mechanism of these GRBs. Our spectro-polarimetric analysis reveals that GRB 160821A has a Poynting flux-dominated jet. On the other hand, GRB 160325A and GRB 160802A have a baryonic-dominated jet with mild magnetization. Furthermore, we observe a rapid change in polarization angle by ~ 90 degrees within the main pulse of very bright GRB 160821A.
Additionly, I will also discuss the spectro-polarimetric analysis of the second brightest burst, GRB 230307A, using data from Fermi, Konus-Wind, and AstroSat. In this analysis, we discovered evidence of a transition from a Baryonic to a Poynting flux-dominated jet composition within the burst’s duration. Our study suggests that the jet composition of GRBs may exhibit a wide range of magnetization, which can be revealed by utilizing spectro-polarimetric investigations of the bright GRBs.
