• DOI:10.1038/nature12762
• Corpus ID: 4447299

Puzzling accretion onto a black hole in the ultraluminous X-ray source M 101 ULX-1

@article{Liu2013PuzzlingAO,
  title={Puzzling accretion onto a black hole in the ultraluminous X-ray source M 101 ULX-1},
  author={Jifeng Liu and Joel N. Bregman and Yu Bai and Stephen Justham and Paul A. Crowther},
  journal={Nature},
  year={2013},
  volume={503},
  pages={500-503}
}

• Jifeng Liu, J. Bregman, +2 authors P. Crowther
• Published 28 November 2013
• Physics
• Nature

There are two proposed explanations for ultraluminous X-ray sources (ULXs) with luminosities in excess of 1039 erg s−1. They could be intermediate-mass black holes (more than 100–1,000 solar masses, ) radiating at sub-maximal (sub-Eddington) rates, as in Galactic black-hole X-ray binaries but with larger, cooler accretion disks. Alternatively, they could be stellar-mass black holes radiating at Eddington or super-Eddington rates. On its discovery, M 101 ULX-1 had a luminosity of 3 × 1039 erg s−1 and a supersoft thermal disk spectrum with an exceptionally low temperature—uncomplicated by photons energized by a corona of hot electrons—more consistent with the expected appearance of an accreting intermediate-mass black hole. Here we report optical spectroscopic monitoring of M 101 ULX-1. We confirm the previous suggestion that the system contains a Wolf-Rayet star, and reveal that the orbital period is 8.2 days. The black hole has a minimum mass of 5, and more probably a mass of 20−30, but we argue that it is very unlikely to be an intermediate-mass black hole. Therefore, its exceptionally soft spectra at high Eddington ratios violate the expectations for accretion onto stellar-mass black holes. Accretion must occur from captured stellar wind, which has hitherto been thought to be so inefficient that it could not power an ultraluminous source.