Outbursts of the intermediate-mass black hole HLX-1: a wind-instability scenario
|dc.contributor.author||van der Helm, E.|
|dc.identifier.citation||Soria, R. and Musaeva, A. and Wu, K. and Zampieri, L. and Federle, S. and Urquhart, R. and van der Helm, E. et al. 2017. Outbursts of the intermediate-mass black hole HLX-1: a wind-instability scenario. Monthly Notices of the Royal Astronomical Society. 469 (1): pp. 886-905.|
We model the intermediate-mass black hole HLX-1, using the Hubble Space Telescope, XMM–Newton and Swift. We quantify the relative contributions of a bluer component, function of X-ray irradiation, and a redder component, constant and likely coming from an old stellar population. We estimate a black hole mass ≈(2+2−1)×104M⊙ , a spin parameter a/M ≈ 0.9 for moderately face-on view and a peak outburst luminosity ≈0.3 times the Eddington luminosity. We discuss the discrepancy between the characteristic sizes inferred from the short X-ray time-scale (R ∼ a few 1011 cm) and from the optical emitter ( Rcosθ−−−−√≈2.2×1013 cm). One possibility is that the optical emitter is a circumbinary disc; however, we disfavour this scenario because it would require a very small donor star. A more plausible scenario is that the disc is large but only the inner annuli are involved in the X-ray outburst. We propose that the recurrent outbursts are caused by an accretion-rate oscillation driven by wind instability in the inner disc. We argue that the system has a long-term-average accretion rate of a few per cent Eddington, just below the upper limit of the low/hard state; a wind-driven oscillation can trigger transitions to the high/soft state, with a recurrence period ∼1 yr (much longer than the binary period, which we estimate as ∼10 d). The oscillation that dominated the system in the last decade is now damped such that the accretion rate no longer reaches the level required to trigger a transition. Finally, we highlight similarities between disc winds in HLX-1 and in the Galactic black hole V404 Cyg.
|dc.publisher||Oxford University Press|
|dc.title||Outbursts of the intermediate-mass black hole HLX-1: a wind-instability scenario|
|dcterms.source.title||Monthly Notices of the Royal Astronomical Society|
This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2017 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.
|curtin.department||Curtin Institute of Radio Astronomy (Physics)|
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