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Description
We study the time-resolved spectral properties of energetic gamma-ray bursts (GRBs) with good high-energy photon statistics observed by the Gamma-Ray Burst Monitor (GBM) onboard the Fermi Gamma-Ray Space Telescope. We aim to constrain in detail the spectral properties of GRB prompt emission on a time-resolved basis and to discuss the theoretical implications of the fitting results in the context of various prompt emission models. Our sample comprises eight GRBs observed by the Fermi GBM in its first five years of mission, with 1keV-1MeV fluence f>1.0x10^-4^erg/cm2 and a signal-to-noise ratio level of S/N>=10.0 above 900keV. We performed a time-resolved spectral analysis using a variable temporal binning technique according to optimal S/N criteria, resulting in a total of 299 time-resolved spectra. We performed Band function fits to all spectra and obtained the distributions for the low-energy power-law index {alpha}, the high-energy power-law index {beta}, the peak energy in the observed {nu}F_{nu}_ spectrum E_p_, and the difference between the low- and high-energy power-law indices {Delta}s={alpha}-{beta}. We also applied a physically motivated synchrotron model, which is a triple power-law with constrained power-law indices and a blackbody component, to test the prompt emission for consistency with a synchrotron origin and obtain the distributions for the two break energies E_b,1_ and E_b,2_, the middle segment power-law index {beta}, and the Planck function temperature kT.
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