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M. Eracleous (Penn State), J. C. Shields (Ohio U.), G. Chartas (Penn State), E. C. Moran (U. C. Berkeley)
We use X-ray observations of galaxies hosting LINERs with Chandra to study their power sources. We find very diverse properties within the group of targets analyzed so far. In two examples the power source is associated with a burst of star formation: NGC 404 has an X-ray-faint nucleus with a soft, thermal spectrum, NGC 4736 harbors a plethora of discrete X-ray sources in and around its nucleus. In a third example (NGC 4579) we find dominant nuclear point source embedded in a very extended, diffuse nebulosity. From their multi-wavelength properties we conclude the following about the three examples mentioned above: the nucleus of NGC 404 is the site of a weak, compact starburst, whose X-ray emission is due to gas heated by stellar winds and supernovae, NGC 4736 is in a recent or aging starburst phase, where the X-ray emission is dominated by a dense cluster of X-ray binaries, and NGC 4579 is powered by accretion onto a supermassive black hole. We detect 39 discrete sources in NGC 4736 and 21 in NGC 4579, most with LX > 1037 erg/s. One source in the disk of NGC 4579 could be an ultraluminous X-ray binary with LX(2-10 keV)=9\times 1039 erg/s, but it could also be a background quasar. The most luminous discrete sources have simple power-law spectra, which along with their luminosities suggest that these are X-ray binaries accreting near or above the Eddington rate for a neutron star. By comparing the luminosity functions of discrete X-ray sources in these and other galaxies we find a potential connection between the age of the stellar population and the slope of the cumulative X-ray source luminosity function: galaxies with primarily old stellar populations have steeper luminosity functions than starburst galaxies. We suggest that this difference results from the contribution of high-mass X-ray binaries from the young stellar population to the upper end of the luminosity function.