The neutron-star low-mass X-ray binary GX 9+1

Figure - An artist's impression of an accreting Low Mass X-ray Binary. The donor star fills its Roche lobe and its material overflows the inner Lagrangian points and accretes on the relativistic star. Due to the large angular momentum of the infalling material an accretion disk is formed around the compact object. Credit: ESA, NASA, and Felix Mirabel (French Atomic Energy Commission and Institute for Astronomy and Space Physics/Conicet of Argentina)

A low-mass X-ray binary (LMXB) contains a neutron star which is accreting material via Roche lobe overflow from a companion star. Due to the high angular momentum of the accretion flow an accretion disc is formed around the compact object.

In a recent paper (van den Berg & Homan 2016) the authors have determined an improved position for the luminous persistent neutron-star low-mass X-ray binary and atoll source GX 9+1 from archival Chandra X-ray Observatory data and they have identified a new near-infrared (NIR) counterpart to GX 9+1 in Ks-band images obtained with the PANIC and FourStar cameras on the Magellan Baade Telescope.

The NIR spectrum is consistent with thermal emission from a heated accretion disk, possibly with a contribution from the secondary. In this respect, GX 9+1 is similar to other bright atolls and the Z sources (typical types of neutron-star sources in low mass X-ray binaries, which present a wide variety in X-ray spectral and variability properties) whose NIR spectra do not show the slope that is expected for a dominant contribution from optically thin synchrotron emission from the inner regions of a jet.

• van den Berg & Homan - 2016 (accepted in Apj) - On the origin of the near-infrared emission from the neutron-star low-mass X-ray binary GX 9+1 (arXiv)