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We present a catalogue of 1696 X-ray sources detected in the massive starforming region (SFR) Cygnus OB2 and extracted from two archival Chandraobservations of the center of the region. A deep source extraction routine,exploiting the low background rates of Chandra observations was employed tomaximize the number of sources extracted. Observations at other wavelengthswere used to identify low count-rate sources and remove likely spurioussources. Monte Carlo simulations were also used to assess the authenticity ofthese sources. We used a Bayesian technique to identify optical or near-IRcounterparts for 1501 (89%) of our sources, using deep observations from theINT Photometric H-alpha Survey, the Two Micron All Sky Survey, and the UKIRTInfrared Deep Sky Survey-Galactic plane Survey. 755 (45%) of these objects havesix-band r', H-alpha, i', J, H, and K optical and near-IR photometry. From ananalysis of the Poisson false-source probabilities for each source we estimatethat our X-ray catalogue includes < 1% of false sources, and an even lowerfraction when only sources with optical or near-IR associations are considered.A Monte Carlo simulation of the Bayesian matching scheme allows this method tobe compared to more simplified matching techniques and enables the varioussources of error to be quantified. The catalogue of 1696 objects presented hereincludes X-ray broad band fluxes, model fits, and optical and near-IRphotometry in what is one of the largest X-ray catalogue of a single SFR todate. The high number of stellar X-ray sources detected from relatively shallowobservations confirms the status and importance of Cygnus OB2 as one of ourGalaxy's most massive SFRs.

The Massive Star Forming Region Cygnus OB2. I. Chandra catalogue of association members