We report the discovery of a near-infrared (NIR) counterpart to the persistent neutron-star low-mass X-ray binary 4U 1705 - 440, at a location consistent with its recently determined Chandra X-ray position. The NIR source is highly variable, with Ks -band magnitudes varying between 15.2 and 17.3 and additional J- and H-band observations revealing color variations. A comparison with contemporaneous X-ray monitoring observations shows that the NIR brightness correlates well with X-ray flux and X-ray spectral state. We also find possible indications of a change in the slope of the NIR/X-ray flux relation among different X-ray states. We discuss and test various proposed mechanisms for the NIR emission from neutron-star low-mass X-ray binaries and conclude that the NIR emission in 4U 1705 - 440 is most likely dominated by X-ray heating of the outer accretion disk and the secondary star. This paper includes data gathered with the 6.5 m Magellan Baade Telescope, located at Las Campanas Observatory, Chile, and the 4 m Blanco Telescope, located at CTIO, Chile.
|Translated title of the contribution||A Variable Near-Infrared Counterpart to the Neutron-Star Low-Mass X-Ray Binary 4U 1705 - 440|
|Pages (from-to)||73 - 80|
|Number of pages||8|
|Publication status||Published - Feb 2009|