Program: GN-2012A-Q-113

We propose near-infrared (NIR) imaging observations of four sub-luminous transient neutron star X-ray binaries during their quiescent state. These sources belong to a new class of X-ray binaries with accretion luminosities 2-3 orders of magnitude fainter than the well studied bright X-ray binaries. The cause of their sub-luminous nature is not known and the current binary evolution models fail to explain these systems. With the known accurate X-ray positions and distance to these sources, we propose NIRI H and Ks observations to search for their NIR counterparts and to generate spectral energy distributions which would help us to estimate the spectral type of their companion. Non-detections of the NIR counterparts would strongly suggest that the donor stars are white dwarfs or brown dwarfs.