The XMM-BCS galaxy cluster survey: I. The X-ray selected cluster catalog   from the initial 6 deg$^2$
  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 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.   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. We derive the cluster log N - log S relation using an approximation to the survey selection function and find it in good agreement with previous studies. We carry out an initial comparison between X-ray luminosity derived masses and masses from optical estimators from the Southern Cosmology Survey for a subset of the cluster sample. Optical masses based on cluster richness and total optical luminosity are found to be significantly higher than the X-ray values.   (abridged) 
R. \v{S}uhada, J. Song, H. B\"ohringer, J. J. Mohr, G. Chon, A.   Finoguenov, R. Fassbender, S. Desai, R. Armstrong, A. Zent...
astro-ph.CO