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We make a detailed time resolved spectroscopy of bright long gamma ray bursts(GRBs) which show significant GeV emissions (GRB 080916C, GRB 090902B, and GRB090926A). In addition to the standard Band model, we also use a modelconsisting of a blackbody and a power-law to fit the spectra. We find that forthe latter model there are indications for an additional soft component in thespectra. While previous studies have shown that such models are required forGRB 090902B, here we find that a composite spectral model consisting of twoblack bodies and a power law adequately fit the data of all the three brightGRBs. We investigate the evolution of the spectral parameters and find severalgeneric interesting features for all three GRBs, like a) temperatures of theblack bodies are strongly correlated to each other, b) flux in the black bodycomponents are strongly correlated to each other, c) the temperatures of theblack body trace the profile of the individual pulses of the GRBs, and d) thecharacteristics of the power law component like the spectral index and thedelayed onset bear a close similarity to the emission characteristics in theGeV regions. We discuss the implications of these results to the possibility ofidentifying the radiation mechanisms during the prompt emission of GRBs.

Time resolved spectral analysis of the prompt emission of long gamma ray bursts with GeV Emission