The HELLAS2XMM Survey. I. The X-Ray Data and the log N-log S Relation

We present the first results from an XMM-Newton serendipitous medium-deep survey, which covers nearly 3 deg2. We detect a total of 1022, 495, and 100 sources, down to minimum fluxes of about 5.9 × 10-16, 2.8 × 10-15, and 6.2 × 10-15 ergs cm-2 s-1, in the 0.5-2, 2-10, and 4.5-10 keV bands, respectively. In the soft band this is one of the largest samples available to date and surely the largest in the 2-10 keV band at our limiting X-ray flux. The measured log N- log S determinations are found to be in good agreement with previous determinations. In the 0.5-2 keV band, we detect a break at fluxes around 5 × 10-15 ergs cm-2 s-1. In the harder bands, we fill in the gap at intermediate fluxes between deeper Chandra and XMM-Newton observations and shallower BeppoSAX and ASCA surveys.