The XMM- Newton - Blanco Cosmology Survey project ( XMM-BCS ) is a coordinated X-ray , optical and mid-infrared cluster survey in a field also covered by Sunyaev-Zel ’ dovich effect ( SZE ) surveys by the South Pole Telescope and the Atacama Cosmology Telescope .
The aim of the project is to study the cluster population in a 14 deg ^ { 2 } field ( center : \alpha \approx 23:29:18.4 , \delta \approx -54:40:33.6 ) .
The uniform multi-wavelength coverage will also allow us for the first time to comprehensively compare the selection function of the different cluster detection approaches in a single test field and perform a cross-calibration of cluster scaling relations .

In this work , we present a catalog of 46 X-ray selected clusters from the initial 6 deg ^ { 2 } survey core .
We describe the XMM-BCS source detection pipeline and derive physical properties of the clusters .
We provide photometric redshift estimates derived from the BCS imaging data and spectroscopic redshift measurements for a low redshift subset of the clusters .
The photometric redshift estimates are found to be unbiased and in good agreement with the spectroscopic values .

Our multi-wavelength approach gives us a comprehensive look at the cluster and group population up to redshifts z \approx 1 .
The median redshift of the sample is 0.47 and the median mass M _ { 500 } \approx 1 \times 10 ^ { 14 } M _ { \odot } ( \sim 2 keV ) .
From the sample , we derive the cluster \log N - \log S using an approximation to the survey selection function and find it in good agreement with previous studies .

We compare optical mass estimates from the Southern Cosmology Survey available for part of our cluster sample with our estimates derived from the X-ray luminosity .
Weak lensing masses available for a subset of the cluster sample are in agreement with our estimates .
Optical masses based on cluster richness and total optical luminosity are found to be significantly higher than the X-ray values .

The present results illustrate the excellent potential of medium-deep , X-ray surveys to deliver cluster samples for cosmological modelling .
In combination with available multi-wavelength data in optical , near-infrared and SZE , this will allow us to probe the dependence of the selection functions on relevant cluster observables and provide thus an important input for upcoming large-area ðmulti-wavelength cluster surveys .