Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006aas...20915504k&link_type=abstract
2007 AAS/AAPT Joint Meeting, American Astronomical Society Meeting 209, #155.04; Bulletin of the American Astronomical Society,
Astronomy and Astrophysics
Astronomy
Scientific paper
We investigate the low luminosity (Lx > 5 10 x 1036 erg s-1) X-ray luminosity functions (XLFs) of low-mass X-ray binaries (LMXBs) determined for two typical old elliptical galaxies, NGC 3379 and NGC 4278. Because both galaxies contain little diffuse emission from hot ISM and no recent significant star formation (hence no high-mass X-ray binary contamination), they provide two of the best homogeneous sample of LMXBs. With deep Chandra ACIS S3 exposures, we present well-determined XLFs which are well represented by a single power-law with a slope (in a differential form) of 1.9 +/0.1. In NGC 4278, we can exclude the break at Lx 5 x 1037 erg s-1 that was recently suggested to be a general feature of LMXB XLFs. In NGC 3379 instead we find a localized excess over the power law XLF at 4 x 1037 erg s-1, but with a marginal significance of 1.6sigma. Because of the small number of luminous sources, we cannot constrain the high luminosity break (at 5 x 1038 erg s-1) found in a large sample of early type galaxies. For our two galaxies, the ratios of the integrated LMXB X-ray luminosities to the optical luminosity differ by a factor of 4, but it is consistent with the general trend of a positive correlation between the X-ray to optical luminosity ratio and the globular cluster specific frequency.
Angelini Leonardo
Brassington Nicola J.
Davies Roger L.
Fabbiano Giuseppina
Gallagher Jay S.
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