The globular cluster mass/low mass X-ray binary correlation: implications for kick velocity distributions from supernovae

¹ Astronomical Institute `Anton Pannekoek', University of Amsterdam, Kruislaan 403, 1098 SJ, Amsterdam, The Netherlands
² School of Physics and Astronomy, University of Southampton, Southampton, Hampshire SO17 1BJ, UK e-mail: tjm@phys.soton.ac.uk
³ Department of Physics and Astronomy, Michigan State University, East Lansing MI, USA

Received: 28 March 2006
Accepted: 27 July 2006

Abstract

Optical and X-ray studies of six nearby galaxies show that the probability a globular cluster will be an X-ray source is consistent with being linearly proportional to its mass. We show that this result is consistent with some recent estimates of the velocity kick distributions for isolated radio pulsars – those which are the sum of two Maxwellians, with the slower distribution at about 100 km s^-1 – so long as a large fraction of the retained binaries are in binary systems with other massive stars. We confirm that over a large sample of galaxies, metallicity is clearly a factor in determining whether a globular cluster will contain an X-ray binary, and we estimate the transformations between color and metallicity for a large number of optical filter combinations. We also show that the core interaction rate is roughly linearly proportional to the stellar mass of a globular cluster for the Milky Way when one bins the clusters by mass.