Using BATSE observations to test the Compton attenuation spectral theory of cosmological gamma-ray bursts

The Compton attenuation theory provides an explanation for the characteristic spectral energy possessed by gamma-ray bursts. It makes several predictions that can be tested with current data, two of which are the characteristic shape of the spectrum and the presence of an X-ray excess. We have performed these tests by fitting the Compton attenuation spectral model to 25 gamma-ray bursts from the BATSE 3B catalog. Minimizing chi(2) with four free parameters, we find values of chi(2) with the same level of significance as the values found for the best-fitting four-parameter models of previous studies. The X-ray upturn makes the chi(2) for the Compton attenuation spectrum smaller than for a comparison spectrum that is a power law over the X-ray energy band. The values of the free parameters derived from the model fits are physically meaningful, and each describes the spectrum over a different frequency band. The absence of a correlation between z and the energy in the comoving frame of the peak of the nu F-nu curve provides support for the model's physical validity. A model tit to a gamma-ray burst's spectrum between 5 and 100 keV gives the redshift of the source; we typically find values of z between 1 and 5. The spread in z are consistent with the spread of redshifts for a broad luminosity function, but the large values require source evolution. Additional tests of the theory are available with current experiments and will be possible with several planned and proposed experiments.