AAS 204th Meeting, June 2004
Session 49 X-ray Binary and ULX Populations in Nearby Galaxies
Topical Session, Wednesday, June 2, 2004, 8:30-10:00am, 10:45am-12:30pm, 2:30-4:00pm, 4:15-6:00pm, 601

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[49.16] X-ray Luminosity Function of LMXB in Early Type Galaxies

D.-W. Kim, G Fabbiano (SAO)

We have derived bias-corrected X-ray luminosity functions (XLFs) of sources detected in a uniformly selected sample of 14 E and S0 galaxies observed with Chandra ACIS-S3. The entire sample yields 985 point-like X-ray sources, with typical detection of 30-140 sources per galaxy. The individual XLFs are statistically consistent with a single power-law of a (differential) XLF slope beta = 1.8 - 2.2 (with a typical error of 0.2-0.3). A break at or near LX,Eddington (of a 1.4 Mo neutron star), as reported in the literature for some of these galaxies, is not required in any case. Given the uniform XLF shape, we have generated a combined, higher statistics, XLF, representative of X-ray sources in elliptical galaxies. Although the combined XLF is marginally consistent with a single power-law (with beta = 2.05 +- 0.07), a broken power-law gives an improved fit. The break luminosity is 4.8 +- 1.2 x 1038 ergs s-1, consistent with the Eddington luminosity of the theoretical maximum mass of a neutron star (3 Mo) or of He-enriched neutron star binaries. Our results imply a different population of high luminosity sources, instead of a beaming effect. We use our results to derive the integrated X-ray luminosity of accreting low-mass X-ray binaries (LMXBs) in each sample galaxy. We confirm that the total X-ray luminosity of LMXBs is correlated with the optical and the near-IR luminosities, but in both cases the scatter exceeds that expected from measurement errors. We find that the scatter in LX(LMXB)/LK is marginally correlated with the specific frequency of globular clusters, suggesting an important role of globular clusters in LMXB evolution, in agreement with the earlier report of White et al.

This work was supported by the CXC contracts, NASA contract NAS8-03060 and NAS8-39073.

The author(s) of this abstract have provided an email address for comments about the abstract: kim@cfa.harvard.edu

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