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Raymond White (University of Alabama)
The X-ray emission from normal elliptical galaxies has two major components: soft (0.2-1 keV) emission from diffuse gas and harder (5-6 keV) emission from populations of accreting stellar X-ray binaries (XRB). The X-ray luminosity of the gaseous component has long been known to exhibit a very large range (factor of 100) for a given optical (stellar) luminosity. The X-ray luminosity of the XRB component was expected to be simply proportional to the optical luminosity of the galaxy, since it is so intimately tied to the stellar population. However, recent ASCA and Chandra observations show that the X-ray luminosity of the binary component exhibits significant scatter (a factor of 3) at a given optical luminosity. This scatter may reflect a range of evolutionary stages in the X-ray binary populations. If so, the XRB X-ray to (galactic) optical luminosity ratio may be used to date the last major bursts of star formation in ellipticals.