THE CORRELATION-FUNCTION OF THE 4-12 KEV X-RAY-BACKGROUND INTENSITY MEASURED WITH THE GINGA LAC

The angular autocorrelation function of the X-ray background in the energy band 4-12 keV has been explored on scales of 2-degrees-25-degrees using 132 exposures obtained with the Large Area Counter (LAC) on board the GINGA satellite. No significant signal is found over the whole range. An upper limit at 2-degrees of 10(-4) is found for the autocorrelation function at the 95 per cent confidence level, significantly lower than previous values obtained in the 2-10 keV band at 3-degrees separation. This upper limit is shown to constrain clustering on scales approximately 10-300 Mpc in the high-redshift (z approximately 0.1-5) Universe, and in particular the cluster-cluster and AGN-AGN correlation functions.