[Paper Review] The XMM-Newton Serendipitous Survey. V. The Second XMM-Newton Serendipitous Source Catalogue

M. G. Watson, A. C. Schröder+48 more|Bristol Research (University of Bristol)|Jul 7, 2008

Astrophysical Phenomena and ObservationsPhysics and Astronomy62 references303 citations

TL;DR

This paper presents the 2XMM catalogue, the largest X-ray source catalogue ever created, derived from 3,491 XMM-Newton pointed observations over 7 years. It contains 246,897 detections of 191,870 unique X-ray sources across >500 deg², with high astrometric accuracy (1.5″ typical) and flux limits down to ~2 × 10⁻¹⁵ erg cm⁻² s⁻¹ in the 0.5–2.0 keV band, enabling deep studies of AGN, clusters, and rare X-ray sources at the flux level dominating the cosmic X-ray background.

ABSTRACT

Aims: Pointed observations with XMM-Newton provide the basis for creating catalogues of X-ray sources detected serendipitously in each field. This paper describes the creation and characteristics of the 2XMM catalogue. Methods: The 2XMM catalogue has been compiled from a new processing of the XMM-Newton EPIC camera data. The main features of the processing pipeline are described in detail. Results: The catalogue, the largest ever made at X-ray wavelengths, contains 246,897 detections drawn from 3491 public XMM-Newton observations over a 7-year interval, which relate to 191,870 unique sources. The catalogue fields cover a sky area of more than 500 sq.deg. The non-overlapping sky area is ~360 sq.deg. (~1% of the sky) as many regions of the sky are observed more than once by XMM-Newton. The catalogue probes a large sky area at the flux limit where the bulk of the objects that contribute to the X-ray background lie and provides a major resource for generating large, well-defined X-ray selected source samples, studying the X-ray source population and identifying rare object types. The main characteristics of the catalogue are presented, including its photometric and astrometric properties .

Motivation & Objective

• To create a comprehensive, high-accuracy X-ray source catalogue from serendipitous detections in XMM-Newton observations.
• To improve upon the first XMM-Newton catalogue (1XMM) by incorporating updated calibration, enhanced processing, and additional source parameters.
• To provide a large, well-defined, X-ray-selected sample covering a significant fraction of the sky at flux levels critical for understanding the X-ray background.
• To support detailed studies of X-ray source populations, including rare object types, via a robust, publicly accessible data resource.
• To enable efficient multi-wavelength follow-up by providing photometric and astrometric precision for source matching with optical and other surveys.

Proposed method

• Reprocessing of EPIC X-ray data from 3,491 public XMM-Newton pointed observations using an improved pipeline with updated instrument calibration.
• Source detection using wavelet-based algorithms to identify point-like and extended X-ray sources across the full energy range (0.2–12.0 keV).
• Astrometric refinement to achieve a typical accuracy of 1.5″ and a best-case accuracy of 0.35″ per source.
• Photometric calibration using cross-comparison between MOS1/MOS2 and pn instruments, achieving ≤5% accuracy for MOS and ≤10% for pn/MOS comparisons.
• Flagging of source reliability using a 'sum flag' parameter to identify high-confidence detections (flag = 0).
• Creation of additional data products, including light curves and spectra, for the brightest 38,320 sources.

Experimental results

Research questions

• RQ1 What is the total number of unique X-ray sources detected in the serendipitous survey of XMM-Newton observations between 2000 and 2007?
• RQ2 What are the photometric and astrometric accuracies of the 2XMM catalogue sources across different instruments and energy bands?
• RQ3 What are the flux limits of the catalogue in different energy bands, and how do they compare to the flux levels that dominate the cosmic X-ray background?
• RQ4 How does the sky coverage of the 2XMM catalogue compare to previous X-ray surveys, particularly in terms of non-overlapping area and total area?
• RQ5 What is the distribution of source types (point-like vs. extended) and how does it inform the population of X-ray sources in the sky?

Key findings

• The 2XMM catalogue contains 246,897 detections drawn from 3,491 XMM-Newton observations, corresponding to 191,870 unique sources.
• The total sky coverage is ~560 deg², with a non-overlapping area of ~360 deg², covering approximately 1% of the celestial sphere.
• The median exposure time is ~16,000 s for MOS1/MOS2 and ~12,500 s for pn per observation.
• The flux limit reaches ~2 × 10⁻¹⁵ erg cm⁻² s⁻¹ in the 0.5–2.0 keV band at 10% sky coverage and ~10 × 10⁻¹⁵ erg cm⁻² s⁻¹ at 90% sky coverage.
• The catalogue achieves a typical astrometric accuracy of 1.5″, with the best sources reaching 0.35″.
• Photometric accuracy is ≤5% for MOS1/MOS2 comparisons and ≤10% for pn/MOS comparisons.