XMM-Newton observations of the Lockman Hole: X-ray source catalogue and number counts^*

¹ Max-Planck-Institut für extraterrestrische Physik, 85478 Garching, Germany e-mail: hbrunner@mpe.mpg.de
² Instituto de Física de Cantabria (CSIC-UC), 39005 Santander, Spain
³ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 0HA, UK
⁴ ESO,Karl-Schwarschild-Strasse 2, 85748 Garching, Germany

Received: 20 April 2007
Accepted: 27 November 2007

Abstract

Context.The Lockman Hole field represents the sky area of lowest Galactic line-of-sight column density  cm^-2. It was observed by the XMM-Newton X-ray observatory in 18 pointings for a total of 1.16 Ms (raw EPIC pn observing time) constituting the deepest XMM-Newton exposure so far. After the removal of time intervals with high particle background, the final effective exposure was 637 ks.

Aims.We present a catalogue of the X-ray sources detected in the central 0.196 deg² of the field and discuss the derived number counts and X-ray colours.

Methods.The analysis was performed using the XMM-SAS data analysis package version 6.0. The detection sensitivity and fraction of spurious detections was calibrated using Monte Carlo simulations.

Results.In the 0.5-2.0 keV band, a sensitivity limit (defined as the faintest detectable source) of  erg cm^-2 s^-1 was reached. The 2.0-10.0 keV band and 5.0-10.0 keV band sensitivity limits were  erg cm^-2 s^-1 and  erg cm^-2 s^-1, respectively. A total of 409 sources above a detection likelihood of 10 (3.9 sigma) were found within a radius of 15′ off the field centre, of which 340, 266, and 98 sources were detected in the soft, hard, and very hard bands, respectively. The number counts in each energy band are in close agreement with results from previous surveys and with the synthesis models of the X-ray background. Six percent of the Compton-thick source candidates have been selected from the X-ray colour-colour diagram. This fraction is consistent with the most recent predictions of X-ray background population synthesis models at our flux limits. We also estimated, for the first time, the relation for Compton-thick AGN.