XMM-Newton SSC: X-ray follow-up & Identification (XID)


Last updated 19-07-2010 by Grant Denkinson; page owner: Jonathan Tedds

The XID Programme

XID programme logo

XMM-Newton logoThe XID programme

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The SSC has a major responsibility towards the identification and follow-up of serendipitous X-ray sources detected in the EPIC CCD cameras, i.e. the XMM-Newton serendipitous sky survey. This is being pursued via the SSC XID programme and is fully described in Watson et al. 2001. The XID programme aims to ensure that the full potential of the XMM-Newton serendipitous source survey is achieved for the benefit of the scientific community.

The programme is exclusively based on public XMM-Newton data, or on XMM-Newton data for which the observer has granted the SSC rights to utilise serendipitous content of the data.

All the results from the programme will be publicly accessible through the XMM-Newton science archive at the SOC.

The main programme components are:


Optical imaging and spectroscopy of well-defined samples from selected XMM-Newton fields, in order to characterise their X-ray source population. Analysis of these samples will be used to establish statistical identification criteria to characterise the complete XID database.

The core programme aims to provide large enough samples to characterise XMM-Newton source populations with sample size sufficient to get 10 objects per sample even for minority objects present at the 1% level.

The core programme (at high galactic latitudes) will be based on samples of 1000 objects in each of 3 broad flux ranges:

FAINT ( > 10-15 erg cm -2 s -1 )
MEDIUM ( > 10-14 erg cm -2 s -1 )
BRIGHT (> 10-13 erg cm -2 s -1 )

There is a comparable programme at low galactic latitudes (PI C.Motch, Strasbourg) - but based on studies of selected regions. The current emphasis of the XID programme is on the MEDIUM FLUX range sample.


More extensive optical imaging programme based on a large fraction of all XMM-Newton fields, providing the optical magnitudes and colours which are essential parameters for statistical identification.

XMM-Newton logoLatest Results & Publications

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The goals of this survey are described in Watson et al. 2001 and include the detailed characterisation of the dominant X-ray source populations (e.g. AGN luminosity functions, absorption distribution and evolution, and the relationship between optical emission line and X-ray spectral properties) and the discovery of new, rare classes of sources.

Results of the XMM-Newton Serendipitous Survey Bright Sample (Della Ceca et al. 04) are published together with the XID Medium Sample (AXIS) X-ray source counts and angular clustering (Carrera et al. 07) with catalogue paper (Barcons et al.) submitted, as part of the core XID spectroscopic identification programme in the Northern hemisphere (AXIS). Further papers based on the medium sensitivity surveys include a study of an X-ray hard, optically bright sample (Page et al. 07) and detailed X-ray spectral analysis of the AXIS extragalactic sample (Mateos et al. 05) while a Galactic Plane sample paper for selected regions (Motch et al.) is in preparation. Further papers are also available from the XMM-Newton Serendipitous Survey Bright Sample webpages. Long term work to obtain multiband optical imaging data for large numbers of XMM-Newton fields is near completion using the INT 4m class telescope with the Wide Field Camera (Yuan et al. 03, Northern hemisphere) and the ESO 2.2m telescope with the Wide Field Imager camera (Dietrich et al. 06, Southern Hemisphere).

In the southern hemisphere we targetted over 3000 sources for the XMM-2dF Wide Angle Serendipitous Survey (XWAS, Tedds et al.), spread evenly over 3 decades in X-ray flux. XWAS makes use of optical multi-fibre spectroscopic identification of optically selected but serendipitously detected XMM-Newton sources using 2dF on the Anglo Australian Telescope and has achieved the XID Medium Sensitivity Sample target of over 1000 identified X-ray sources brighter than F(0.5-4.5keV) > 10-14 erg/cm2/s. This is an unsurpassed resource with which to investigate the AGN population around the break in the X-ray source counts. Forthcoming papers will include detailed X-ray spectral analysis of the identified BLAGN (Mateos et al.) and stacking of all XID BLAGN spectra (Corral et al.) together with other sub samples such as normal galaxies (Xu et al.), Type II QSOs (Krumpe et al.) and rare objects such as BALQSOs (Page et al.) uniquely discovered in this kind of large area survey. Ultimately we wish to pursue a wider statistical characterisation of the growing serendipitous XMM-Newton catalogues including the newly released 2XMM based on such a medium sensitivity identified sample as a training set.

XMM-Newton logoProgramme Details

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XID field selection

XMM-Newton fields are selected for the XID programme using the following criteria, adopted to ensure that the serendipitous source content can be properly utilised:

(for those fields already observed)
Full frame observation in thin or medium filters.
> 20 ks for the extragalactic sample, > 15 ks for Galactic.
large, spatially extended objects avoided (e.g. SNR, cluster of galaxies, large nearby galaxies).
field should not include any optical source bright enough to dominate deep optical imaging (e.g. very bright star).
data must be outside of proprietary rights or have the SSC_XID flag set to "Y" in the proposal database.
observability for ground-base observations.

Ground-based observations

  • Optical imaging:
    • INT 2.5m with WFC
    • ESO 2.2m with WFI
    • TNG 3.5m with OIG
    • Subaru 8.3m with SuprimeCam & FOCAS
  • IR imaging:
    • INT 2.5m with CIRSI
    • UKIRT 3.8m with UFTI, UIST
  • Optical spectroscopy:
    • WHT 4.2m with ISIS
    • WHT 4.2m with WYFFOS/AUTOFIB2
    • TNG 3.5m with DOLORES
    • NOT 2m with ALFOSC
    • Subaru 8.3m with FOCAS
    • AAT 4m with 2dF

A large fraction of the observing time for the XID programme in the Northern Hemisphere has been allocated to the `AXIS' programme, a Canaries Islands International Time Project (ITP) in 2000/2001 & 2001/2002. Additional allocations include INT WFC & ESO WFI imaging, multi fibre optical spectroscopy in the South on the AAT with 2dF, Halpha imaging on CFHT, Magellan 6m spectroscopy etc. etc.

Fields under study

The table linked below provides a preliminary list of the fields currently under study within the XID programme.

XID fields under study

XMM-Newton logoPublic data

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The first data from the XID Programme has now been released.

Link to public data page

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Links to other sites that may be useful: