GSC2 S230011017253 , the SIMBAD biblio

This paper is the first of a series dedicated to the X-ray properties of the young open cluster NGC6231. Our data set relies on an XMM-Newton campaign of a nominal duration of 180ks and reveals that NGC6231 is very rich in the X-ray domain too. Indeed, 610 X-ray sources are detected in the present field of view, centered on the cluster core. The limiting sensitivity of our survey is approximately 6x10^–15erg/cm2/s but clearly depends on the location in the field of view and on the source spectrum. Using different existing catalogues, over 85% of the X-ray sources could be associated with at least one optical and/or infrared counterpart within a limited cross-correlation radius of 3" at maximum. The surface density distribution of the X-ray sources presents a slight N-S elongation. Once corrected for the spatial sensitivity variation of the EPIC instruments, the radial profile of the source surface density is well described by a King profile with a central density of about 8 sources per arcmin² and a core radius close to 3.1-arcmin. The distribution of the X-ray sources seems closely related to the optical source distribution. The expected number of foreground and background sources should represent about 9% of the detected sources, thus strongly suggesting that most of the observed X-ray emitters are physically belonging to NGC6231. Finally, beside a few bright but soft objects - corresponding to the early-type stars of the cluster - most of the sources are relatively faint (∼5x10^–15erg/cm2/s) with an energy distribution peaked around 1.0-2.0keV.