We test the models of synchrotron emission presented in Part I of this series ( Lloyd & Petrosian , these proceedings ; [ 8 ] ) against the distributions and evolution of GRB spectral parameters ( particularly the low energy index , \alpha ) .
With knowledge of the E _ { p } distribution and the correlation between \alpha and E _ { p } presented in [ 8 ] , we show how to derive the expected distribution of \alpha from fits to optically thin synchrotron spectra , and compare this with the observed distribution .
We show that there is no difficulty explaining bursts below the “ line of death ” , \alpha < -2 / 3 , and that these bursts indicate that the spectrum of accelerated electrons must flatten or decline at low energies .
Bursts with low energy spectral indices that fall above this limit are explained by the synchrotron self-absorption frequency entering the lower end of the BATSE window .
Finally , we discuss a variety of spectral evolution behavior seen in GRBs and explain this behavior in the context of synchrotron emission from internal shocks .