PRODUCING THE UNIVERSAL SPECTRUM OF COSMOLOGICAL GAMMA-RAY BURSTS WITH THE KLEIN-NISHINA CROSS-SECTION

A power-law spectrum attenuated through Compton scattering by an optic ally thick medium produces spectra that have a characteristic energy o f several hundred keV. Add a redshift, and one finds that this model c an qualitatively reproduce the color-color diagrams found for individu al gamma-ray bursts. This model is easily tested through model fits to burst spectra and through comparisons of the parameters derived from model fits to the limits on parameters derived from the burst log N - log P(max) curve. The heavy attenuation makes the amount of energy rel eased in the burst almost-equal-to 10(3) times larger than is inferred from the observed flux. The requirements of high optical depth and no photon-photon pair creation place a lower limit on the size of the sc attering region. This size suggests that the attenuation occurs in gia nt molecular clouds in the cores of galaxies. This indicates that gamm a-ray bursts are probably from supermassive black holes. If the Lorent z factor of the radiation source is large, the optical depth, and ther efore the hardness ratio of a burst, can change over the duration of t he burst.