Constraining the mass of accreting black holes in ultraluminous X-ray sources with ultrafast outflows
Apr 26, 20175 pages
Published in:
- Mon.Not.Roy.Astron.Soc. 469 (2017) 1, L99-L103
- Published: Jul 21, 2017
e-Print:
- 1704.08255 [astro-ph.HE]
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Abstract: (Oxford University Press)
The nature of ultraluminous X-ray sources (ULXs) – off-nuclear extragalactic sources with luminosity, assumed isotropic, ≳10^39 erg s^−1 – is still debated. One possibility is that ULXs are stellar black holes (BHs) accreting beyond the Eddington limit. This view has been recently reinforced by the discovery of ultrafast outflows at ∼0.1–0.2c in the high-resolution spectra of a handful of ULXs, as predicted by models of supercritical accretion discs. Under the assumption that ULXs are powered by super-Eddington accretion on to BHs, we use the properties of the observed outflows to self-consistently constrain their masses and accretion rates. We find masses ≲100 M_⊙ and typical accretion rates ∼10^−5 M_⊙ yr^−1, i.e. ≈10 times larger than the Eddington limit calculated with a radiative efficiency of 0.1. However, the emitted luminosity is only ≈10 per cent beyond the Eddington luminosity, because most of the energy released in the inner part of the accretion disc is used to accelerate the wind, which implies radiative efficiency ∼0.01. Our results are consistent with a formation model where ULXs are BH remnants of massive stars evolved in low-metallicity environments.Note:
- 5 pages, 2 figures, 1 table, accepted for publication in MNRAS Letters
- accretion, accretion discs
- black hole physics
- binaries: close
- X-rays: binaries
References(46)
Figures(2)