The XMM-Newton wide-field survey in the COSMOS field. II. X-ray data and the log N-log S relations

We present data analysis and X-ray source counts for the first season of XMM-Newton observations in the COSMOS field. The survey covers ∼2 deg ² within the region of sky bounded by 09 ^h57 ^m30 ^s < R.A. < 10 ^h03 ^m30 ^s, 01°27′30″ < decl. < 02°57′ 30″ with a total net integration time of 504 ks. A maximum likelihood source detection was performed in the 0.5-2, 2-4.5, and 4.5-10 keV energy bands, and 1390 pointlike sources were detected in at least one band. Detailed Monte Carlo simulations were performed to fully test the source-detection method and to derive the sky coverage to be used in the computation of the log N-log S relations. These relations were then derived in the 0.5-2, 2-10, and 5-10 keV energy bands, down to flux limits of 7.2 × 10 ^-16 ergs cm ^-2 s ^-1,4.0 × 10 ^-15 ergs cm ^-2 s ^-1, and 9.7 × 10 ^-15 ergs cm ^-2 s ^-1, respectively. Thanks to the large number of sources detected in the COSMOS survey, the log N-log S curves are tightly constrained over a range of fluxes which were poorly covered by previous surveys, especially in the 2-10 and 5-10 keV bands. The 0.5-2 and 2-10 keV differential log N-log S relations were fitted with a broken power-law model which revealed a Euclidean slope at the bright end and a flatter slope (α ∼ 1.5) at faint fluxes. In the 5-10 keV energy band a single power law provides an acceptable fit to the observed source counts with a slope α ∼ 2.4. A comparison with the results of previous surveys shows good agreement in all the energy bands under investigation in the overlapping flux range. We also notice a remarkable agreement between our log N-log S relations and the most recent model of the X-ray background.