With the Australian Square Kilometre Array Pathfinder (ASKAP) we monitored the black hole candidate X-ray binary MAXI J1535--571 over seven epochs from 21 September to 2 October 2017. Using ASKAP observations, we studied the HI absorption spectrum from gas clouds along the line-of-sight and thereby constrained the distance to the source. The maximum negative radial velocities measured from the HI absorption spectra for MAXI J1535--571 and an extragalactic source in the same field of view are −69±4 km s−1 and −89±4 km s−1, respectively. This rules out the far kinematic distance (9.3−0.6+0.5 kpc), giving a most likely distance of 4.1−0.5+0.6 kpc, with a strong upper limit of the tangent point at 6.7−0.2+0.1 kpc. At our preferred distance, the peak unabsorbed luminosity of MAXI J1535--571 was >78 per cent of the Eddington luminosity, and shows that the soft-to-hard spectral state transition occurred at the very low luminosity of 1.2 -- 3.4 × 10−5 times the Eddington luminosity. Finally, this study highlights the capabilities of new wide-field radio telescopes to probe Galactic transient outbursts, by allowing us to observe both a target source and a background comparison source in a single telescope pointing.
@article{arxiv.1905.08497,
title = {An HI absorption distance to the black hole candidate X-ray binary MAXI J1535-571},
author = {Jaiverdhan Chauhan and James C. A. Miller-Jones and Gemma E. Anderson and Wasim Raja and Arash Bahramian and Aidan Hotan and Balt Indermuehle and Matthew Whiting and James R. Allison and Craig Anderson and John Bunton and Baerbel Koribalski and Elizabeth Mahony},
journal= {arXiv preprint arXiv:1905.08497},
year = {2019}
}
Comments
Revised after favorable referee report from MNRAS Letters