Discovery of the near-infrared counterpart to the luminous neutron-star low-mass X-ray binary GX 3+1

Abstract

Using the High Resolution Camera onboard 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_s=15.8+-0.1 mag star as the counterpart is based on the presence of a Br-gamma emission line in a NIR spectrum taken with the FIRE 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 ~ 1e36 to 1e37 erg/s) than GX 3+1, where optically-thin synchrotron emission from a jet probably dominates the NIR flux.

Accepted for publication in ApJ

References in corpus (2)

• Interstellar Extinction Law toward the Galactic Center II: V, J, H, and Ks Bands
• Evidence for a jet contribution to the optical/infrared light of neutron star X-ray binaries

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• Machine Learning Classification of COSMOS2020 Galaxies: Quiescent vs. Star-Forming
• AstroSat observation of rapid Type-I thermonuclear burst from the low mass X-ray binary GX 3+1
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• COSMOS2025: A Machine Learning Census of Massive Quiescent Galaxies at $2.5<\text{z}<5$