XMM-Newton Users Handbook

B. XMM-Newton Survey Science Centre (SSC)

Because of its large throughput and good spatial resolution, pointed observations with the XMM-Newton EPIC X-ray cameras reach very faint X-ray flux limits ($\approx$ a few $\times 10^{-15}$ erg cm$^{-2}$ s$^{-1}$, 0.2-12 keV, in typical observations). At these fluxes, each XMM-Newton EPIC field at both high and low galactic latitudes contains substantial numbers of ``serendipitous'' X-ray sources. Pointed XMM-Newton observations thus provide a ``serendipitous'' X-ray survey (the ``XMM-Newton Serendipitous Sky Survey'', see Watson et al., 2001, A&A, 365, L51 and Watson, 1998, Astr. Nachr., 319, 117) which, like previous surveys, is expected to make a major impact in a number of front-line areas of astrophysics, a fact that provided one of the original motivations for the SSC concept within the XMM-Newton project.

The role of the SSC in this area is to coordinate the follow-up of the serendipitous content of XMM-Newton observations in order to ensure that this valuable resource can be exploited effectively by the community. The key initial step is the `identification' of the X-ray sources, i.e., classification into different object types. Literally identifying every one of the $\sim$200,000 XMM-Newton serendipitous sources is not a realistic task, nor a sensible approach. Instead, the emphasis of the SSC XID Program is on the characterization of the XMM-Newton source population through the detailed follow-up of well-defined, small subsamples (as outlined below). The XID Program thus aims to bring together the XMM-Newton data themselves, existing catalogue and archival material and new ground-based observational data in an integrated fashion.

The overall XID Program has two main components:

The ``Core Program''

consisting of complete identifications of selected high galactic latitude X-ray samples based primarily on optical imaging and spectroscopy. The results from this program are being used to ``characterize'' the content of the XMM-Newton serendipitous survey. The Core Program also includes a parallel study for the low galactic latitude sky.

The ``Imaging Program''

which aims to obtain optical photometry and colors for a substantial fraction of all XMM-Newton fields. The rationale is based on the fact that a combination of X-ray flux and X-ray colors (from the XMM-Newton data) and optical magnitude and optical colors (e.g. from new ground-based observations) provide the key parameters which make possible an accurate `probabilistic' identification of the XMM-Newton sources. This is possible using the results from the Core Program which characterize the XMM-Newton source populations, thus providing the link, in a statistical sense, between the source identification and properties and these basic parameters.

The entire program is based on samples of serendipitous X-ray sources drawn from pointed XMM-Newton observations that are in the public domain, or are made available to the SSC by the observation PI.

The initial phases of the XID Program are now nearing completion. Publications describing various aspects of the program and initial results include: Watson et al., 2001, A&A, 365, L51; Barcons et al., 2002, A&A, 382, 522; Watson et al., 2003, ADASS XII (ASP Conference Series), Vol. 295; Yuan, W., 2003, Astr. Nachr., 324, 178; Caccianiga, A. 2004, A&A, 416, 901; Della Ceca et al., 2004, A&A, 428, 383; Carrera et al., 2007, A&A, 469, 27

Up-to-date status information for the XID program can be found at:
http://xmmssc-www.star.le.ac.uk/. This page also provides links to public pages maintained by other SSC institutions involved in the Program.

The XID program is designed to support the community's access to, and exploitation of, the serendipitous data from XMM-Newton, and as such all the results will be made public through the XMM-Newton Science Archive. An initial release of XID program WFC/INT images is now available in the XMM-Newton Science Archive.