Are Supernova Kicks Responsible for X-Ray Binary Ejection from Young Clusters?

Abstract

Recent Chandra observations of interacting and starburst galaxies have led us to investigate the apparent correlation between the positions of young star clusters and the positions of Chandra point sources. Assumed to be X-ray binaries (XRBs), these point sources do not seem to coincide with the massive (~105 Msolar), young (1-50 Myr) stellar clusters that can easily form systems capable of such emission. We use a sophisticated binary evolution and population synthesis code (StarTrack) and a simplified cluster model to track both the X-ray luminosity and the position of XRBs as a function of time. These binaries are born within the cluster potential with self-consistent positions and velocities, and we show that a large fraction (~=70%) can be ejected from the parent as a result of supernova explosions and associated systemic velocities. For brighter sources and cluster masses below ~106 Msolar, we find that the average number of bright XRBs per cluster remains near or below unity, consistent with current observations.