SAADA    The XMM-Newton Survey Science Centre XID Programme

The SSC's XID programme is a follow-up and identification project designed to ensure that the potential of the XMM-Newton serendipitous survey can be exploited by the community in the context of a wide range of scientific programmes. Its main elements are a number of complementary sub-programmes designed to obtain the identifications for well-defined samples of X-ray sources drawn from selected XMM-Newton fields using optical/IR spectroscopy. The programme is also supported by a substantial imaging programme, needed for the selection of the spectroscopic targets, but which is also an important resource in its own right given the large sky area and hence X-ray source sample it covers.
One of the principal objectives of the programme is to obtain completely identified samples which can be used to characterise the overall XMM-Newton source population sufficiently well that the basic X-ray and optical parameters can be used to assign a statistical identification for a large fraction of all the sources in the XMM-Newton serendipitous source catalogue.
The XID programme started in mid-2000. Most of the programme is now complete. The XIDResult Database collects together the main results from the XID programme in a uniform way, providing access to the individual source identifications and the key optical and X-ray data for each object.
Currently in the XIDResult Database contains 3 key XID programme subsamples, the XBS (XID bright flux sample), the XMS (XID medium flux sample) and the GPS (Galactic source sample), all of which have been published or are in press. The main optical references for each of these subsamples are as follows:
Further details of these and related components of the XID programme are given below. We plan to incorporate the additional XID programme component results in the database in the near future.
a) The XID bright flux sample (XBS/BSS/HBSS programmes)
The XMM-Newton Bright Survey (XBS) consists of two flux-limited samples of X-ray selected serendipitous sources at high galactic latitude (|b| > 20 deg): the XMM bright serendipitous survey sample (BSS, 389 sources) and the XMM hard bright serendipitous survey sample (HBSS, 67 sources, with 56 sources in common with the BSS sample) having an EPIC MOS2 count rate limit, corrected for vignetting, of 10-2 cts/s and 2x10-3 cts/s in the 0.5-4.5 keV and 4.5-7.5 keV energy bands, respectively; the flux limit is ~7x10-14 erg cm-2 s-1 in both energy selection bands. The details on the XMM-Newton fields selection strategy and the source selection criteria of the XMM BSS and HBSS samples are discussed in Della Ceca et al. (2004) while a description of the optical data and analysis, of the optical classification scheme and the optical properties of the extragalactic sources identified so far is presented in Caccianiga et al.(2007) and Caccianiga et al. (2008). The optical and X-ray properties of the Galactic population are discussed in Lòpez-Santiago et al. (2007), while the X-ray spectral properties of the AGN population are described in Corral et al. (2010). Other main results of the XBS project are discussed in Severgnini et al. (2003), Caccianiga et al. (2004), Galbiati et al. (2005) and Della Ceca et al. (2008).
b) The XID medium flux sample (XMS, AXIS & XWAS programmes)
The XMS sample contains identifications for 318 XMM-Newton sources in the north with fluxes > 10-14 erg cm-2 s-1 in the 0.5-4.5 keV band, representing a completeness of >90% overall (Barcons et al., 2007). This is one of the largest and most completely identified samples of medium flux sources yet assembled. The XMS sources are drawn from the larger AXIS sample (1433 sources) which has been used, inter alia, to characterize the X-ray source counts and angular clustering (Carrera et al., 2007) and the stacked spectra of X-ray sources (Corral et al., 2008). The XWAS sample, which began later, consists of ~1000 spectroscopic IDs of southern XMM-Newton sources obtained with the AAT 2dF. Selected results for ~100 AGN have been published (Garcet et al., 2007), and have been incorporated into other studies, eg. Corral et al. (2008); Krumpe et al. (2008), but the main XWAS catalogue paper is in preparation.
c) The XID Galactic source sample (GPS/XGPS programmes)
The GPS includes a sample of >1000 XMM-Newton sources in both shallow and deep XMM-Newton fields. The identification rate is much lower than at high Galactic latitudes, as expected, but the programme has already produced a range of new results on the stellar population, γ-Cas analogues and isolated neutron stars. The main catalogue paper will be resubmitted in the near future once revisions to the modeling of the stellar X-ray population are completed.
d) The XID Imaging Programme
This programme consists of several hundred deep multi-colour optical images taken with the INT Wide Field Camera (~230 XMM-Newton fields typically in three [g' r' i'] colours but with a subset in five [U g' r' i' Z]) and with the ESO 2.2m WFI (~60 fields in BVRI). Processing, reduction and quality control of the INT WFC images and object catalogues is complete (but some work remains, see below). The ESO WFI images have been processed and reduced, but production of photometrically calibrated catalogues faces some major challenges and is not yet complete. The Imaging Programme covers over 50 sq.deg. of the XMM-Newton sky and reaches ~2 magnitudes deeper than SDSS (with a typical ID rate of 80% in contrast to 50-60% achieved with SDSS). It thus represents a key resource which can provide an X-ray/optical catalogue of >20,000 X-ray sources, a powerful resource for extending a range of current studies, eg. of distant clusters and high-redshift quasars.