A deep XMM-Newton serendipitous survey of a middle-latitude area

II. New deeper X-ray and optical observations

¹ INAF-IASF, Istituto di Astrofisica Spaziale e Fisica Cosmica “G.Occhialini”, via Bassini 15, 20133 Milano, Italy e-mail: novara@iasf-milano.inaf.it
² Università di Pavia, Dipartimento di Fisica Teorica e Nucleare, via Ugo Bassi 6, 27100 Pavia, Italy
³ Mullard Space Science Laboratory, University College London, Holmbury St Mary, Dorking, RH56NT, Dorking, UK
⁴ European Southern Observatory, Karl Schwarzschild Str.2, 85748 Garching, Germany
⁵ Isaac Newton Group of Telescopes, Apartado de correos 321, 38700 Santa Cruz de La Palma Tenerife, Spain
⁶ Argelander-Institut für Astronomie, Auf dem Hügel 71, 53121 Bonn, Germany
⁷ IUSS – Istituto Universitario di Studi Superiori, Viale Lungo Ticino Sforza 56, 27100 Pavia, Italy

Received: 16 July 2008
Accepted: 21 March 2009

Abstract

Context. The radio-quiet neutron star 1E1207.4-5209 has been the target of several XMM-Newton observations, with a total exposure of ~350 ks. The source is located at intermediate galactic latitude (), i.e. in a sky region with an extremely interesting mix of both galactic and extra-galactic X-ray sources.

Aims. The aim of our work is to investigate the properties of both the intermediate-latitude galactic and extra-galactic X-ray source populations in the 1E1207.4-5209 field.

Methods. We performed a coherent analysis of the whole XMM-Newton  observation data set to build a catalogue of serendipitous X-ray sources detected with high confidence and to derive information on the source flux, spectra, and time variability. In addition, we performed a complete multi-band (UBVRI) optical coverage of the field with the Wide Field Imager  (WFI) of the ESO/MPG 2.2 m telescope (La Silla) to search for candidate optical counterparts to the X-ray sources, down to a V-band limiting magnitude of ~24.5.

Results. From the combined observation data set we detected a total of 144 serendipitous X-ray sources. We find evidence that the source  distribution may be different from those computed either in the Galactic plane or at high galactic latitudes. Thanks to the refined X-ray positions and to the WFI observations, we found candidate optical counterparts for most of the X-ray sources in our compilation. For most of the brightest ones we proposed a likely classification based on both the X-ray spectra and the optical colours.

Conclusions. Our results indicate that at intermediate galactic latitude the X-ray source population is dominated by the extra-galactic component, but with a significant contribution from the galactic component in the soft energy band, below 2 keV.