The globular cluster population of low-luminosity X-ray sources

More than thirty low-luminosity X-ray sources (with L(x) less than or similar to 10(34.5) erg s(-1)) have now been discovered in globular clusters. The nature of these sources is still unclear. One important question is how the number of sources scales with cluster parameters such as central density or cluster mass. Because the detected sample is biased towards the brightest sources, such an analysis must rely on knowledge of the underlying luminosity function. We present here a statistical analysis of current observations of dim cluster X-ray sources. We determine the luminosity function to be dN/dL proportional to L(-1.5), and find that the number of dim X-ray sources per cluster scales less steeply with core density than predicted by the two-body tidal capture model, just as do cluster pulsars.