The Spectrum of Diffuse Cosmic X-Rays 7.7-113 keV

An X-ray telescope aboard the OSO-III satellite provided data from which we derive the intensity of diffuse cosmic X-rays in five energy bands between 77 and 113 keV. A ngle power law cannot represent our data in this energy range The 1 year of satellite operation has allowed a determination of systematic effects, so that the four lowest energy points have an accuracy of about 3 percent They fit a powemlaw spectrum of index 1.7 + 0.1 which "breaks" at 42 I 4 keV to become 3.0 I 0.3. The normalization constant gives an intensity of 15.2 photons (cm2 sec sterad keV)-' at 1 keV. A more complicated spectral shape suggested by Brecher and Morrison fits the present data very well and provides a better extrapolation to data at keV and a few MeV than does the power law.