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M.S. Sipior, M. Eracleous, S. Sigurdsson (Penn State University)
We present results from a detailed modeling of high mass (>4 M\odot) binary star populations. We study the formation of X-ray binaries after a starburst, looking at both the rate at which various categories of XRBs are created, and their mass transfer properties. From this, we calculate expected X-ray luminosities and hardness ratios (using spectral templates motivated by observations). Cumulative luminosity functions are constructed for the sample and compared to those in observations of star-forming galaxies such as Circinus and NGC 4736. A synthetic x-ray spectrum of the total population is also constructed. The time evolution of these results is of particular importance; in particular, we note that the evolution of the integrated X-ray luminosity from a short burst of star formation remains relatively constant for several hundred Myr after the burst, as different XRB classes become dominant and then fade. In contrast, the integrated X-ray spectrum of the XRB population does change dramatically, starting off quite hard, and softening over a period of 10--20 Myr, as the HMXB population gives way to LMXBs.
We also study the long-term fate of HMXBs after they become binary compact objects. Closely-bound systems that survive a second supernova can become significant sources of gravitational radiation. We calculate the R6 rate (mergers per Myr per Milky Way galaxy) of a number of coalescence channels, normalizing our results to the Galactic supernova rate (after estimating a binarity fraction). Natal asymmetric kicks are shown to dramatically reduce the rate of NS-NS coalescence. While NS-NS mergers have been thought to be more common, we show that BH-BH mergers may in fact dominate the detected signal, given the larger wave amplitude produced by these systems. This prediction will be directly testable with the completion of the LIGO instrument next year.