Revealing a new symbiotic X-ray binary with Gemini Near-infrared Integral Field Spectrograph

Abstract

We use K-band spectroscopy of the counterpart to the rapidly variable X-ray transient XMMU J174445.5-295044 to identify it as a new symbiotic X-ray binary. XMMU J174445.5-295044 has shown a hard X-ray spectrum (we verify its association with an INTEGRAL/Imager on-Board the INTEGRAL Satellite 18-40 keV detection in 2013 using a short Swift/X-Ray Telescope observation), high and varying N_H, and rapid flares on time-scales down to minutes, suggesting wind accretion on to a compact star. We observed its near-infrared counterpart using the Near-infrared Integral Field Spectrograph at Gemini-North, and classify the companion as ∼M2 III. We infer a distance of 3.1^{+1.8}_{-1.1} kpc (conservative 1σ errors), and therefore calculate that the observed X-ray luminosity (2-10 keV) has reached to at least 4 × 10³⁴ erg s^-1. We therefore conclude that the source is a symbiotic X-ray binary containing a neutron star (or, less likely, black hole) accreting from the wind of a giant.