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

摘要

We present data analysis and X- ray source counts for the first season of XMM- Newton observations in the COSMOS field. The survey covers similar to 2 deg(2) within the region of sky bounded by 09(h)57(m)30(s) < R. A. < 10(h)03(m)30(s), 01 degrees 27'30 '' < decl. < 02 degrees 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 keVenergy 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 keVenergy bands, down to flux limits of 7.2x10(-16) ergs cm(-2) s(-1), 4.0x10(-15) ergs cm(-2) s(-1), and 9.7x10(-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 (alpha similar to 1.5) at faint fluxes. In the 5-10 keVenergy band a single power law provides an acceptable fit to the observed source counts with a slope alpha similar to 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.