Spectral Analysis of Bright Gamma Ray Bursts

We present the time integrated and time resolved spectral analysis of a sample of bright bursts selected from the BATSE archive. We fitted four different spectral models to the time integrated and time resolved spectra of the flux pulses. We point out that the found (marginal) differences in the parameter distributions can be ascribed to the different spectral shape of the employed models and that a smoothly curved model best fits the observed spectra. We characterize the spectral shape of bright bursts and compare the low energy slope of the fitted spectra with the prediction N(E) = E^{-2/3} of the synchrotron theory, finding that this limit is violated in a considerable number of time resolved spectra around the peaks, both during the rise and decay phase.