On the Chandra X-ray sources in the Galactic center

Recent deep Chandra surveys of the Galactic center region have revealed the existence of a faint, hard X-ray source population. While the nature of this population is unknown, it is likely that several types of stellar objects contribute. For sources involving binary systems, accreting white dwarfs and accreting neutron stars with main-sequence companions have been proposed. Among the accreting neutron star systems, previous studies have focused on stellar wind-fed sources. In this paper, we point out that binary systems in which mass transfer occurs via Roche lobe overflow (RLOF) can also contribute to this X-ray source population. A binary population synthesis study of the Galactic center region has been carried out, and it is found that evolutionary channels for neutron star formation involving the accretion-induced collapse of a massive ONeMg white dwarf, in addition to the core collapse of massive stars, can contribute to this population. The RLOF systems would appear as transients with quiescent luminosities, above 2 keV, in the range from 10³¹ to 10³² ergs s^-1. The results reveal that RLOF systems primarily contribute to the faint X-ray source population in the Muno et al. survey and that wind-fed systems can contribute to the less sensitive Wang et al. survey. However, our results suggest that accreting neutron star systems are not likely to be the major contributor to the faint X-ray source population in the Galactic center.