The XMM‐Newton Wide‐Field Survey in the COSMOS Field. II. X‐Ray Data and the log N ‐log S Relations

Abstract

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 deg2 within the region of sky bounded by 09h57m30s < R.A. < 10h03m30s, 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.