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J. A. Irwin, J. N. Bregman (University of Michigan), C. L. Sarazin (University of Virginia)
The sub-arcsecond spatial resolution of the Chandra X-ray Observatory has paved the way for the study of the X-ray binary population of nearby galaxies, which in early-type systems are primarily low-mass X-ray binaries (LMXBs). Here, I present some initial results on the spectral characteristics and luminosity distribution function of the LMXBs in a sample of early-type galaxies. The spectrum of the LMXBs is substantially harder than that of the hot gas that also resides in these galaxies, but comparable to LMXBs in our own Galaxy. For the galaxies studied so far, there is either a break or cut-off in the luminosity function at a luminosity of ~2e38 ergs/s, which is approximately the Eddington luminosity of a 1.4 solar mass accreting neutron star. If this break is a universal feature of galaxies, it might be used as a distance estimator. At lower X-ray luminosities, the LMXB population is remarkably similar from galaxy to galaxy, suggesting that the high end of the initial mass function was very similar in early-type systems in the past. I discuss a method of using this similarity to further constrain the distances to these galaxies. Finally, I discuss the implications of the tendency of LMXBs to be preferentially located within globular clusters.