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J. A. Irwin, J. N. Bregman (University of Michigan), C. L. Sarazin (University of Virginia)
We present results from a Chandra ACIS-S observation of the nearby S0/Sa galaxy NGC1291. Previous ROSAT PSPC observations revealed that the spectrum of this galaxy strongly resembled that of a class of elliptical and S0 galaxies that had unusually low X-ray--to--optical luminosity ratios. In these types of galaxies it was believed that the X-ray emission was largely from a collection of low mass X-ray binaries (LMXBs), with possibly a contribution from a hot interstellar medium. Chandra is allowing us for the first time to resolve large numbers of LMXBs in galaxies to determine the relative breakdown of LMXB to gaseous emission. Within the inner 2' of the bulge of NGC1291, 48 sources are resolved which comprise 67% of the total emission. The remaining emission is soft and diffuse. The luminosity distribution function of the LMXBs shows a break around the Eddington luminosity of a 1.4 solar mass neutron star, a result also seen in NGC4697. Another break is seen around 2.5 X 1037 ergs s-1, coinciding with a break found for the bulge of M31 by previous ROSAT HRI observations. It is possible that these breaks might be exploited as an independent distance indicator to nearby galaxies.
This work was supported by Chandra Fellowship grant PF9-10009, awarded through the Chandra Science Center. The Chandra Science Center is operated by the Smithsonian Astrophysical Observatory for NASA under contract NAS8-39073.