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We present a systematic analysis of the spectral and temporal properties of17 GRBs co-detected by GBM and LAT on board the Fermi satellite by May 2010. Weperformed a time-resolved spectral analysis of all the bursts with the finesttemporal resolution allowed by statistics, in order to avoid temporal smearingof different spectral components. We found that the time-resolved spectra of 14out of 17 GRBs are best modeled with the Band function over the entire Fermispectral range, which may suggest a common origin for emissions detected by LATand GBM. GRB 090902B and GRB 090510 require the superposition between an MeVcomponent and an extra power law component, with the former having a sharpcutoff above E_p. For GRB 090902B, this MeV component becomes progressivelynarrower as the time bin gets smaller, and can be fit with a Planck function asthe time bin becomes small enough. In general, we speculate thatphenomenologically there may be three elemental spectral components : (I) aBand-function component (e.g. in GRB 080916C) that extends in a wide energyrange and does not narrow with reducing time bins, which may be of thenon-thermal origin; (II) a quasi-thermal component (e.g. in GRB 090902B) withthe spectra progressively narrowing with reducing time bins; and (III) anothernon-thermal power law component extending to high energies. The spectra ofdifferent bursts may be decomposed into one or more of these elementalcomponents. We compare this sample with the BATSE sample and investigate somecorrelations among spectral parameters. We discuss the physical implications ofthe data analysis results for GRB prompt emission, including jet compositions(matter-dominated vs. Poynting-flux-dominated outflow), emission sites(internal shock, external shock or photosphere), as well as radiationmechanisms (synchrotron, synchrotron self-Compton, or thermal Comptonupscattering).

A Comprehensive Analysis of Fermi Gamma-Ray Burst Data. I. Spectral Components and Their Possible Physical Origins of LAT/GBM GRBs