Measuring The Distance To The Black Hole Candidate X-Ray Binary Maxi J1348-630 Using Hi Absorption

We present neutral hydrogen (HI) absorption spectra of the black hole candidate X-ray binary (XRB) MAXI J1348-630 using the Australian Square Kilometre Array Pathfinder (ASKAP) and MeerKAT. The ASKAP HI spectrum shows a maximum negative radial velocity (with respect to the local standard of rest) of -31 +/- 41cm s(-1) for MAXI J1348-630, as compared to -50 +/- 41cm s(-1) for a stacked spectrum of several nearby extragalactic sources. This implies a most probable distance of 2.2(-0.6)(+0.5) kpc for MAXI J1348-630, and a strong upper limit of the tangent point distance at 5.3 +/- 0.1 kpc. Our preferred distance implies that MAXI J1348-630 reached 17 +/- 10 per cent of the Eddington luminosity at the peak of its outburst, and that the source transited from the soft to the hard X-ray spectral state at 2.5 +/- 1.5 per cent of the Eddington luminosity. The MeerKAT HI spectrum of MAXI J1348-630 (obtained from the older, low-resolution 4k mode) is consistent with the re-binned ASKAP spectrum, highlighting the potential of the eventual capabilities of MeerKAT for XRB spectral line studies.