Time resolved spectral analysis of bright gamma ray bursts

Abstract

We present the time integrated and time resolved spectral analysis of a sample of bright bursts selected with Fpeak 20 phot cm 2 s 1 from the BATSE archive. We fitted four dierent spectral models to the pulse time integrated and time resolved spectra. We compare the low energy slope of the fitted spectra with the prediction of the synchrotron theory (predicting photon spectra softer than N(E) / E 2=3 ), and test, through direct spectral fitting, the synchrotron shock model. We point out that dierences in the parameters distribution can be ascribed to the dierent spectral shape of the models employed and that in most cases the spectrum can be described by a smoothly curved function. The synchrotron shock model does not give satisfactory fits to the time averaged and time resolved spectra. Finally, we derive that the synchrotron low energy limit is violated in a considerable number of spectra both during the rise and decay phase around the peak.