Multi-Wavelength Identification of Galactic X-ray Sources

Abstract

We explore the production and observation of high energy (X-ray and ultraviolet/UV) radiation in the context of Galactic, compact binary systems. At the end of the stellar lifecycle, a star collapses into one of three compact objects (COs) depending on the mass at the time of collapse: a white dwarf (WD), neutron star (NS) or a black hole (BH). These dense, stellar remnants are often found in close orbits (a â¼ Râ) with another star whose atmosphere can flow to the CO, releasing massive amounts of gravitational energy in the process. These systems are known as X-ray binaries (XRBs) for the complex interaction of the stellar pair and constituent matter manifests in bright X-ray luminosities of L_X â¼ 10^32 â 10^42 erg/s making them among the brightest X-ray emitters in the sky. The formation and distribution of XRBs is still not fully understood, in part because a homogeneous sample of Galactic XRBs is not yet available due to selection effects biased towards bright and transient sources. The Galactic Bulge Survey (GBS) was designed to identify a large, quiescent population and found 1640 unique X-ray sources in 12 square degrees near the Galactic Plane. Most systems are still unclassified, specifically those in dense optical or infrared (IR) fields where the true source of X-ray emission can be visually ambiguous. We avoid this ambiguity for 269 of 1640 systems by using UV data from GALEX to identify the correct optical/IR counterparts, making use of the low GALEX surface density (and high correlation with X-ray sources). We then create and model spectral energy distributions for each system. We identify a new group of 15 â 25 likely compact binary systems by their excess UV fluxes and classify â¼ 150 GBS systems as nearby, chromospherically-active stars. Finally, we discuss our results in the context of the GBS and suggest future research directions.