Sample of optically unidentified X-ray binaries in the Galactic bulge: constraints on the physical nature from infrared photometric surveys

We report on archival near-infrared and mid-infrared observations of seven persistent X-ray sources situated in the Galactic bulge, using data from the UK Infrared Telescope (UKIRT) Infrared Deep Sky Survey (UKIDSS), the Spitzer Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE) and the Wide-field Infrared Survey Explorer (WISE) all-sky survey. We were able to successfully identify or provide upper flux limits for the systems SAX J1747.0-2853, IGR J17464-2811, AX J1754.2-2754, IGR J17597-2201, IGR J18134-1636, IGR J18256-1035 and Ser X-1 and constrain the nature of these systems. In the case of IGR J17597-2201, we present arguments that the source accretes matter from the stellar wind rather than via Roche-lobe overflow of the secondary. We suggest that, at its X-ray luminosity of 10^{34 - 35} erg s^-1, we are probing the poorly known class of wind-fed low-mass X-ray binaries (LMXBs).