Two Thousand X-ray Stars in the Central 20 pc of the Galaxy

Abstract

We present a catalog of 2357 point sources detected during 620 ks of Chandra observations of the 17 × 17 arcminutes field around Sgr A*. This field encompasses a physical area of 40 × 40 parsecs at 8 kpc. The completeness limit of the sample at the Galactic Center is ≈1031 erg s−1 (2–8 keV), while the detection limit is an order of magnitude lower. We estimate that 20–100 of the observed sources are background AGN. The spectra of the majority of the Galactic Center sources are very hard and are best described by a power law (E−Γ) with photon index Γ < 1. Such hard spectra are only seen from magnetically accreting white dwarfs (polars and intermediate polars) and neutron stars (pulsars). The spatial density of the Galactic Center X-ray sources falls off as R−2, similar to that of the infrared stars in the field. This highlights the possibility that these X-ray sources can be used to study the history of star formation at the Galactic Center. The log(N) − log(S) distribution of the Galactic Center sources is extremely steep, such that point sources could account for all of the previously reported diffuse emission if the number counts extend down to 1029 erg s−1 with the same slope. However, there are numerous fllamentary structures in the field that also contribute to the total flux, which implies that the luminosity distribution between 2–8 keV must turn over below our completeness limit.