The Isotropy of the Diffuse Cosmic X-Rays Determined by Oso-Iii

An X-ray telescope aboard the 080-Ill satellite has scanned almost the entire sky during a 1-year period and has searched for anisotropies in the diffuse component. After excluding known galactic sources, the extragalactic cosmic X-rays between 7.7 and 38 keV have no component of peak-to-peak amplitude greater than 2 percent that varies smoothly over the entire sky. This limit to any 24-hour variation restricts the velocity of the Earth to less than 800 km in any direction relative to a rest frame in which the X-rays would appear isotropic. For about one-quarter of the sky, the upper4imit confidence of 95 percent to an inhomogeneity within the half-response aperture of 115 radius equals 4 percent. At 10 keY there exists a 10 percent increase in counting rate associated with the galactic plane of equivalent line-source strength 0.012 + 0.004 photons (cm2 sec keV rad) 1. The upper limit to X-rays associated with a galactic halo equals 3 percent.