DISCOVERY OF THE NEAR-INFRARED COUNTERPART TO THE LUMINOUS NEUTRON-STAR LOW-MASS X-RAY BINARY GX 3+1

• Main Authors: van den Berg, Maureen (Author), Homan, Jeroen (Contributor), Fridriksson, Joel K. (Author), Linares, Manuel Alegret (Author)
• Other Authors: MIT Kavli Institute for Astrophysics and Space Research (Contributor)
• Format: Article
• Language: English
• Published: Institute of Physics/American Astronomical Society, 2015-02-19T20:19:25Z.
• Subjects: Article
• Online Access: Get fulltext

 Using the High Resolution Camera on board the Chandra X-ray Observatory, we have measured an accurate position for the bright persistent neutron star X-ray binary and atoll source GX 3+1. At a location that is consistent with this new position, we have discovered the near-infrared (NIR) counterpart to GX 3+1 in images taken with the PANIC and FourStar cameras on the Magellan Baade Telescope. The identification of this K[subscript s] = 15.8 ± 0.1 mag star as the counterpart is based on the presence of a Br γ emission line in an NIR spectrum taken with the Folded-port InfraRed Echelette spectrograph on the Baade Telescope. The absolute magnitude derived from the best available distance estimate to GX 3+1 indicates that the mass donor in the system is not a late-type giant. We find that the NIR light in GX 3+1 is likely dominated by the contribution from a heated outer accretion disk. This is similar to what has been found for the NIR flux from the brighter class of Z sources, but unlike the behavior of atolls fainter (LX ≈ 10[superscript 36]-10[superscript 37] erg s[superscript -1]) than GX 3+1, where optically thin synchrotron emission from a jet probably dominates the NIR flux.