THE SUBDEGREE ANGULAR STRUCTURE OF THE X-RAY SKY AS SEEN BY THE GINGA SATELLITE

An autocorrelation function analysis of two sets of scan data taken with the Ginga Large Area Counter around the North Ecliptic and North Galactic poles respectively has been performed down to separations of 0.2-degrees. No significant deviation from isotropy is found below 2-degrees and the corresponding 95 per cent confidence upper limits [W(0.2-degrees-2-degrees) < (1.5-0.5) x 10(-3)] are used to constrain clustering of AGN in the framework of specific models for the origin of the X-ray background. A marginal negative signal is seen at 3-degrees as in previous work, which if interpreted in terms of the presence of voids in the nearby X-ray Universe leads to radii of 0.5-degrees to 1-degrees and filling factors of less than 60 per cent for these structures. Finally, we use the lack of anisotropies below 2-degrees to limit the contribution of source clustering to the observed P(D) fluctuations in the X-ray sky. This implies that all fluctuations have to be attributed to source counts and leaves open the mismatch between soft and intermediate-energy extragalactic X-ray source counts.