Population Synthesis of X-Ray Sources at the Galactic Center

We are exploring the evolution of massive binary star populations for a nuclear starburst occurring in the conditions similar to the Milky Way Galaxy, in its central part, on a timescale of 10 Myr. A computer code is applied allowing for computing, by using Monte Carlo simulations, the evolution of a large ensemble of binary systems, with proper accounting for spin evolution of magnetized neutron stars (NSs). Our results include a number of X-ray transients (each consisting of a NS plus main-sequence star), superaccreting black holes (BHs), and binaries consisting of a BH plus a supergiant, all as functions of time. We find that by 7 Myr after such a starburst one expects ≈1 X-ray source with a BH (Cyg X-t type), ≈1 SS 433-like source (BH in the regime of superaccretion), and ≈37 transient sources with a NS, all to be within the central t kpc or so. An interesting result that can be considered a specific starburst feature is that the ratio of the number of systems like 55 433 to the number of X-ray transients is about t: 100, compared with 1: 1000 characteristic of the average ratio in the Galactic field. The ratio of the total number of X-ray sources containing a BH (of Cyg X-1 plus 55 433 types) to the number of X-ray transients with NSs turns out to be a sensitive function of the age of the starburst, and its computed value ≈0.04 is consistent with observations.