Xray source counts in the 2XMM serendipitous source catalogue

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X-ray source counts in the 2XMM serendipitous
source catalogue

• Silvia Mateos
• University of Leicester

R.S. Warwick, M.G. Watson, G. Stewart, J. Tedds
University of Leicester F.J.Carrera, J. Ebrero
Instituto de Fisica de Cantabria G. Lamer
AIP-Potsdam
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Why do we want to study the source counts
distributions?

• The logN-logS contains information on
• Cosmological evolution of sources
• spectral evolution
• distribution of X-ray absorption and its
  dependence on X-ray luminosity
• and redshift
• Because identifications can only be obtained for
  relatively small samples
• of objects, source counts are frequently used to
  get insight into the
• above topics

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Aims of this work

• Constrain source counts distributions with
  unprecedented accuracy at both soft and hard
  energies over a broad range of X-ray fluxes
• Study variations of the source counts shape
• at different energies
• for different populations of sources (e.g. X-ray
  colour selection)
• Test predictions from XRB synthesis models

• Select large enough sample of X-ray
  observations
• to overcome effects of cosmic variance
• obtain large number of sources over broad range
  in flux and at
• different energies

• The second XMM-Newton serendipitous source
  catalogue 2XMM (release date Aug07) ideal data
  base

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The sample

• Selected 1129 2XMM observations
• ?b?gt20 deg
• pn data
• GTI(pn) gt 5 ksec
• avoided fields with bright
• and extended targets

sky distribution of observations
equatorial coordinates
clean exposure time distribution
galactic coordinates
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X-ray catalogue

• Simultaneous source detection of the five 2XMM
  energy bands
• Selected objects with pn ML15 (5? significance)
• Targets removed from catalogue
• Observations visually screened

2XMM energy bands
(0.5-1.0) (1.0-2.0)
(2.0-4.5) (4.5-12.)
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Sensitivity of our survey
? corrected for overlapping of observations

• Empirical sensitivity maps calculation (see
  Carrera07)

?TOT137.4 deg2

• minimum area of 2 deg2

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2XMM 0.5-2 keV source counts
Integral normalised to euclidean slope
AGNclus Gilli07
AGN only Gilli07
2XMM coverage
Agreement within few with previous
XMM-Newton/Chandra results Overall good agreement
with predictions from latest XRB synthesis model
marginal excess of 2XMM counts at bright
fluxes stars marginal excess of model
predictions at faint fluxes
References AXIS (Carrera07), ChaMP (Kim06),
XMM-LSS(Chiappetti05), COSMOS(Cappelluti07), CDF
(Bauer04)
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2XMM 2-12 keV source counts
Integral normalised to euclidean slope
AGNclus Gilli07
AGN only Gilli07
2XMM coverage
In the main there is reasonable agreement between
current results Overall good agreement with
predictions from latest XRB synthesis model
marginal excess of model predictions at faint
fluxes
References AXIS (Carrera07), ChaMP (Kim06),
AMSS(Ueda05), COSMOS(Cappelluti07), CDF (Bauer04)
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2XMM source countsall energy bands together
Integral source counts normalised to euclidean
slope
Integral source counts
Energy band flux
Energy band flux
Unprecedented accuracy on source counts
determination on all energy bands Different
shapes for different energy bands
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logN-logS break in energy bands
Integral normalised to euclidean slope
HR2 vs 0.5-1 keV flux
All count rates converted to same energy band
HR2 vs 1-2 keV flux

• Increasing contribution from hard sources at
  higher energies and at faint fluxes

z0.7, ?1.8 NH1022cm-2 HR2gt0.48
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2XMM source counts for sources with different
X-ray colours
Separate samples of sources using X-ray colours
0.5-2 keV differential source counts
more turnover of source counts for sources with
soft X-ray colours Different spectral and
absorption evolution
z0.7, ?1.8 NH1022cm-2
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Summary

• Source counts distributions with unprecedented
  accuracy obtained from
• 1129 observations from the 2XMM catalogue
  covering 137 deg2 at high
• galactic latitudes at different X-ray energies
  and over a broad range in flux
• The 2XMM source counts showed
• excellent agreement with previous surveys in the
  0.5-2 keV band
• reasonable agreement in the 2-12 keV band
• Reasonable agreement between 2XMM source counts
  and predictions from XRB models although
• 2XMM source counts break occurs at higher fluxes
• Detected variations of the source counts shape
• in different energy bands
• New population of hard sources
• for sources with different X-ray colours
• Different spectral and absorption evolution
• All this can be used to extract essential
  information on spectral properties and evolution
  of XRB sources

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