[Normal Galaxies, Clusters of Galaxies -- Oral ]

Modeling X-ray binary populations in elliptical galaxies.

Tassos Fragos, Northwestern University
Kalogera, V. (Northwestern University), Fabbiano, G. (Harvard-Smithsonian Center for Astrophysics)

X-ray binaries are unique astrophysical laboratories as they carry information about many complex physical processes such as star formation, compact object formation, and evolution of interacting binary systems. Motivated by deep Chandra observations of extra-galactic populations of X-ray binaries, I will present theoretical models for the formation and evolution of populations of low-mass X-ray binaries (LMXBs) in the two elliptical galaxies NGC 3379 and NGC 4278. The models are calculated with the recently updated StarTrack code, assuming only a primordial galactic field LMXB population. StarTrack is an advanced population synthesis code that has been tested and calibrated using detailed binary star calculations and incorporates all the important physical processes of binary evolution. The simulations are targeted to modeling and understanding the origin of the X-ray luminosity functions (XLFs) of point sources in these galaxies. For the first time we explore the population XLF in luminosities below 10E37 erg/s, as probed by the most recent observational results. Furthermore, I will present a physically motivated and self-consistent prescription for the modeling of transient neutron star LMXB properties, such as duty cycle, outburst duration and recurrence time, and compare the model transient LMXB population to the Chandra X-ray survey of the two ellipticals, which revealed several transient sources. Finally, I will briefly talk about an ongoing project towards developing a new advanced computational tool for the study of X-ray binary populations formed in both galactic fields and dense stellar clusters.