Diffuse cosmic x rays arise from Compton collisions between galactic leakage electrons and the 2.7°K thermal background photons in extragalactic space. Assuming that the break seen in the electron spectra within normal galaxies is intrinsic to the cosmic-ray sources, we obtain detailed agreement with the observed x-ray spectral shape and intensity using only parameters obtained from radio observations. This serves to verify most of the properties of the microwave blackbody radiation.

• Received 11 July 1969

DOI:https://doi.org/10.1103/PhysRevLett.23.802