The correlation function of the 4-12 keV X-ray background intensity measured with the GINGA LAC

Abstract

The angular autocorrelation function of the X-ray background in the energy band 4–12 keV has been explored on scales of 2∘−25∘ 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∘of10−4 is found for the autocorrelation function at 95 per cent confidence level, significantly lower than previous values obtained in the 2–10 keV band at 3° separation. This upper limit is shown to constrain clustering on scales about ∼10 − 300 Mpc in the high-redshift (z∼0.1−5) universe, and in particular the cluster–cluster and AGN–AGN correlation functions.