Evidence for the ultra-compact nature of IGR J17062-6143

J. V. Hernandez Santisteban, V. Cuneo, N. Degenaar, J. van den Eijnden, D. Altamirano, M. N. Gomez, D. M. Russell, R. Wijnands, R. Golovakova, M. T. Reynolds, J. M. Miller

Published 2018-01-09Version 1

We present a multi-wavelength study of the persistent low-luminosity neutron star low-mass X-ray binary \igr. The multi-epoch photometric UV to NIR spectral energy distribution (SED) is consistent with an accretion disc $F_{\nu}\propto\nu^{1/3}$. The SED modelling of the accretion disc allowed us to estimate an outer disc radius of $R_{out}=3.9^{+1.9}_{-1.1} \times 10^{9}$ cm and a mass-transfer rate $\dot{m}=1.7^{+6.9}_{-1.2}\times10^{-9}$ M$_{\odot}$ yr$^{-1}$, consistent with both theoretical and observational estimates of ultra-compact X-ray binaries (UCXB). In combination with empirical X-ray/NIR relationships, we estimate the orbital period of the system to be $\sim0.4-1$ hr. In addition, we obtained a low-resolution optical spectrum which revealed a blue continuum and no emission lines. The lack of hydrogen in the spectrum and the size of the accretion disc provide further evidence for an ultra-compact nature of this system.