Population Synthesis of Ultraluminous X-ray Sources with Magnetized Neutron Stars

A model of a population of ultraluminous X-ray sources with magnetized neutron stars (NULXs) in a spiral galaxy with a star formation history as in the thin disk of theMilkyWay is constructed by the hybrid population synthesis method. First, based on analytical approximations (BSE code), we compute a set of close binary systems (CBSs), potential precursors of NULXs, and, then, the evolution with mass accretion onto magnetized neutron stars (NSs) is computed by the MESA evolutionary code. The accretion rate onto NSs and the X-ray luminosity of sources are calculated for the models of sub- or supercritical disks and disks with advection. During accretion onto magnetized NSs, super-Eddington luminosities L-X > 10(38) erg s(-1) are reached already at the subcritical stage, when the energy release at the inner boundary of the disk defined by the NS magnetosphere is sub-Eddington one. Our calculations show that the standard evolution of CBSs, given the peculiarities of accretion onto magnetized NSs, allows the observed properties of NULXs (X-ray luminosities, NS spin periods, CBS orbital periods, and optical component masses) to be quantitatively explained without requiring additional model assumptions about the collimation of X-ray emission from NSs with a high observed super-Eddington luminosity. In a model galaxy with a star formation rate similar to 5 M-circle dot yr(-1) there can be several NULXs. The detection of a powerful wind from NULXs with L-X similar to 10(41) erg s(-1) may suggest supercritical accretion onto magnetized NSs.