2021MNRAS.501L..60C

We present neutral hydrogen (H I) 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 H I spectrum shows a maximum negative radial velocity (with respect to the local standard of rest) of -31 ± 4 km s^–1 for MAXI J1348-630, as compared to -50 ± 4 km s^–1 for a stacked spectrum of several nearby extragalactic sources. This implies a most probable distance of 2.2^+0.5_–0.6 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 H I 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.