Counterparts to the Nuclear Bulge X-ray Source Population

We present an initial matching of the source positions of the Chandra Nuclear Bulge X-ray sources to the new UKIDSS-GPS near-infrared survey of the Nuclear Bulge. This task is made difficult by the extremely crowded nature of the region, despite this, we find candidate counterparts to ∼ 50% of the X-ray sources. We show that detection in the J-band for a candidate counterpart to an X-ray source preferentially selects those candidate counterparts in the foreground whereas candidate counterparts with only detections in the H and K-bands are more likely to be Nuclear Bulge sources. We discuss the planned follow-up for these candidate counterparts. The Wang et al. (2002) and Muno et al. (2003) Chandra surveys of the Nuclear Bulge revealed a large population of weak, hard point-like X-ray sources that could account for up to 10% of the previously observed " diffuse " X-ray emission from the Nuclear Bulge. Numerous studies have tried to characterise these newly discovered X-ray sources of the Nuclear Bulge surveys based on their X-ray properties. Pfahl et al. (2002) suggest that a large fraction may be wind-accreting neutron stars with high mass companions. Muno et al. (2003, 2006) and Ruiter et al. (2006) propose that they could be white dwarfs accreting from main sequence counterparts (cataclysmic variables, polars and intermediate polars). Willems & Kolb (2003) and Liu & Li (2006) believe them to be neutron stars with low mass companions and Wu et al. (2007) have speculated that they could be isolated neutron stars and black holes accreting from the interstellar medium. However, the weak nature of the sources means that positive identification of the majority of the sources is impossible based 1