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[52.01] Are All Low-Mass X-ray Binaries Formed Within Globular Clusters?

J. A. Irwin, J. N. Bregman (University of Michigan)

Recent Chandra observations of nearby early-type galaxies have revealed that a significant fraction (30%--70%) of low-mass X-ray binaries (LMXBs) within these galaxies reside within globular clusters. Yet whether all LMXBs form within globular clusters is still an open question. Using a sample of early-type galaxies observed with Chandra, we address this issue further. For each galaxy, we have determined the total X-ray luminosity, L_X, from the sum of the individual LMXBs within each galaxy and compared this value to the number of globular clusters in the galaxy (or more specifically, L_X/L_B,gal vs. the globular cluster specific frequency, S_N). We find a strong correlation between L_X/L_B,gal and S_N, confirming that a significant number of LMXBs are formed within globular clusters. However, the y-intercept of the L_X/L_B,gal vs. S_N relation is not zero, indicating that there is a population of LMXBs that was not formed within globular clusters. We place constraints on the relative importance of the non-globular cluster LMXB population and discuss the implications of our result.

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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.