Models for Low-Mass X-Ray Binaries in Elliptical Galaxies NGC3379 and NGC4278

Abstract

We present theoretical models for populations of low‐mass X‐ray binaries in two elliptical galaxies: NGC3379 and NGC4278. The models are calculated with the recently updated StarTrack code (Belczynski et al. 2007), and are targeted to modeling and understanding the origin of the X‐ray luminosity functions (XLF) in these galaxies. For the first time we explore the population XLF down to luminosities of 3×1036 erg s−1, as probed by the most recent observational results (Kim et al. 2006). We consider models for the formation and evolution of low‐mass X‐ray binaries (LMXB) in galactic fields with different common envelope efficiencies, stellar wind prescriptions and initial mass functions. We identify models that produce an XLF in excellent agreement with the observations both in shape and number of systems at a specific luminosity. We also find that the treatment of the outburst luminosity of transient systems remains a crucial parameter for the determination of the XLF as the modeled populations are dominat...