USING BATSE OBSERVATIONS TO TEST THE COMPTON ATTENUATION SPECTRAL THEORY OF COSMOLOGICAL GAMMA-RAY BURSTS

The Compton attenuation theory provides an explanation for the charact eristic spectral energy possessed by gamma-ray bursts. It makes severa l predictions that can be tested with current data, two of which are t he characteristic shape of the spectrum and the presence of an X-ray e xcess. We have performed these tests by fitting the Compton attenuatio n spectral model to 25 gamma-ray bursts from the BATSE 3B catalog. Min imizing chi(2) with four free parameters, we find values of chi(2) wit h the same level of significance as the values found for the best-fitt ing four-parameter models of previous studies. The X-ray upturn makes the chi(2) for the Compton attenuation spectrum smaller than for a com parison spectrum that is a power law over the X-ray energy band. The v alues of the free parameters derived from the model fits are physicall y meaningful, and each describes the spectrum over a different frequen cy 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 t he model's physical validity. A model tit to a gamma-ray burst's spect rum between 5 and 100 keV gives the redshift of the source; we typical ly find values of z between 1 and 5. The spread in z are consistent wi th the spread of redshifts for a broad luminosity function, but the la rge values require source evolution. Additional tests of the theory ar e available with current experiments and will be possible with several planned and proposed experiments.