A VARIABLE NEAR-INFRARED COUNTERPART TO THE NEUTRON-STAR LOW-MASS X-RAY BINARY 4U 1705 - 440

• Main Authors: Homan, Jeroen (Contributor), Kaplan, David L. (Contributor), van den Berg, Maureen (Author), Young, Andrew J. (Author)
• Other Authors: MIT Kavli Institute for Astrophysics and Space Research (Contributor)
• Format: Article
• Language: English
• Published: Institute of Physics/American Astronomical Society, 2015-03-26T14:23:21Z.
• Subjects: Article
• Online Access: Get fulltext

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.
United States. National Aeronautics and Space Administration (Hubble Fellowship grant #01207.01-A, Space Telescope Science Institute)