Measuring the distance to the black hole candidate X-ray binary MAXI J1348-630 using HI absorption

TL;DR

This study uses HI absorption spectra from ASKAP and MeerKAT to determine the distance to the black hole candidate X-ray binary MAXI J1348-630, providing insights into its luminosity and spectral state transitions during outburst.

Contribution

First measurement of MAXI J1348-630's distance using HI absorption spectra from ASKAP and MeerKAT, demonstrating the potential of MeerKAT for XRB spectral line studies.

Findings

Distance to MAXI J1348-630 is approximately 2.2 kpc.

MAXI J1348-630 reached about 17% of Eddington luminosity at outburst peak.

Source transitioned from soft to hard state at about 2.5% of Eddington luminosity.

Abstract

We present 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 $-31\pm4$ km s$^{-1}$ for MAXI J1348-630, as compared to $-50\pm4$ 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 $5.3\pm0.1$ kpc. Our preferred distance implies that MAXI J1348-630 reached $17\pm10$ % 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 $2.5\pm1.5$ % 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.