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/IBIS 18-40 keV detection in 2013 using a short Swift/XRT observation), high and varying NH, and rapid flares on timescales down to minutes, suggesting wind accretion onto a compact star. We observed its near-infrared counterpart using the Near-infrared Integral Field Spectrograph (NIFS) at Gemini-North, and classify the companion as ~ M2 III. We infer a distance of 3.1−1.1+1.8 kpc (conservative 1-sigma errors), and therefore calculate that the observed X-ray luminosity (2-10 keV) has reached to at least 4×1034 erg/s. 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.
@article{arxiv.1403.7231,
title = {Revealing a new symbiotic X-ray binary with Gemini NIFS},
author = {Arash Bahramian and Jeanette C. Gladstone and Craig O. Heinke and Rudy Wijnands and Ramanpreet Kaur and Diego Altamirano},
journal= {arXiv preprint arXiv:1403.7231},
year = {2015}
}