The XMM-Newton serendipitous survey: III. The AXIS X-ray source counts and angular clustering

Context. Recent results have revised upwards the total X-ray background (XRB) intensity below∼10 keV, therefore an accurate determination of the source counts is needed. There are also contradicting results on the clustering of X-ray selected sou rces. Aims. We have studied the X-ray source counts in four energy bands soft (0.5-2 keV), hard (2-10 keV), XID (0.5-4.5 keV) and ultra-hard (4.5-7.5 keV), to evaluate the contribution of s ources at different fluxes to the X-ray background. We have also studied the angular clustering of X-ray sources in those bands. Methods. AXIS (An XMM-Newton International Survey) is a survey of 36 high Galactic latitu de XMM-Newton observations covering 4.8 deg 2 and containing 1433 serendipitous X-ray sources detected with 5-σ significance. This survey has similar depth to the XMM-Newton catalogues and can serve as a pathfinder to explore their poss ibilities. We have combined this survey with shallower and deeper surveys, and fitted the source counts with a Maximu m Likelihood technique. Using only AXIS sources, we have studied the angular correlation using a novel robust technique. Results. Our source counts results are compatible with most previous samples in the soft, XID, ultra-hard and hard bands. We have improved on previous results in the latter band. The fractions of the XRB resolved in the surveys used in this work are 87%, 85%, 60% and 25% in the soft, hard, XID and ultra-hard bands, respectively. Extrapolation of our source counts to zero flux are n ot enough to saturate the XRB intensity. Only galaxies and/or absorbed AGN may be able contribute the remaining unresolved XRB intensity. Our results are compatible, within the errors, with recent r evisions of the XRB intensity in the soft and hard bands. The maximum fractional contribution to the XRB comes from fluxes within a bout a decade of the break in the source counts (∼ 10 −14 cgs), reaching ∼50% of the total in the soft and hard bands. Angular clustering (widely distributed over the sky and not confined to a few dee p fields) is detected at 99-99.9% significance in the soft and XID bands , with no detection in the hard and ultra-hard band (probably due to the smaller number of sources). We cannot confirm the detection o f significantly stronger clustering in the hard-spectrum ha rd sources. Conclusions. Medium depth surveys such as AXIS are essential to determine the evolution of the X-ray emission in the Universe below 10 keV.