Predicting ultraluminous X-ray source demographics from geometrical beaming

Middleton, Matthew; King, Andrew

doi:10.1093/mnrasl/slx079

Cited by 44 publications

(43 citation statements)

References 26 publications

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“…To explain the observed range of the blackbody luminosity, both neutron stars and stellar-mass black holes are required as the accretor. This is in line with the fact that a considerable fraction of ULXs may contain neutron stars (Middleton & King 2017) but they cannot be easily detected with current telescopes (Pintore et al 2017). A possible bimodal feature in the distribution of the blackbody luminosity is seen, but at low significance.…”

Section: Discussionsupporting

confidence: 69%

Evidence for Optically Thick, Eddington-limited Winds Driven by Supercritical Accretion

Zhou

Feng

et al. 2019

ApJ

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Supercritical accretion onto compact objects powers a massive wind that is optically thick and Eddingtonlimited. If most of the hard X-rays from the central disk are obscured by the wind, the source will display a blackbody-like spectrum with a luminosity scaled with the mass of the compact object. From the Chandra archive of nearby galaxies, we selected a sample of luminous and very soft sources and excluded contaminations from foreground objects and supernova remnants. They are found to be preferentially associated with late-type galaxies. The majority of sources in our sample are either too hot or too luminous to be explained by nuclear burning on the surface of white dwarfs, and are argued to be powered by accretion. The most likely explanation is that they are due to emission from the photosphere of a wind driven by supercritical accretion onto compact objects. Their blackbody luminosity ranges from ∼10 37 to nearly 10 40 erg s −1 , indicative of the presence of both neutron stars and stellar-mass black holes. The blackbody luminosity also shows a possible bimodal distribution, albeit at low significance, peaked around the Eddington limit for neutron stars and stellar-mass black holes, respectively. If this can be confirmed, it will be smoking gun evidence that supercritical accretion powers thick winds. Based on a wind model, the inferred mass accretion rate of these objects is around a few hundred times the Eddington rate, suggesting that they may be intermediate between the canonical ultraluminous X-ray sources and SS 433 in terms of the accretion rate.

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Section: Discussionsupporting

confidence: 69%

Evidence for Optically Thick, Eddington-limited Winds Driven by Supercritical Accretion

Zhou

Feng

et al. 2019

ApJ

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“…The low count rates due to being extragalactic sources, the presence of spin-up and orbital modulation, and possible transience in pulsations make them very challenging to detect, however, and the proportion of ULXs that contain neutron star accretors as opposed to black holes is still an open question (e.g. King & Lasota 2016;Middleton & King 2017), especially since their broadband spectra are otherwise indistinguishable from the rest of the ULX population (e.g. Koliopanos et al 2017;Pintore et al 2017;Walton et al 2018).…”

Section: Introductionmentioning

confidence: 99%

The (Re)appearance of NGC 925 ULX-3, a New Transient ULX

Earnshaw

Heida

Brightman

et al. 2020

ApJ

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We report the discovery of a third ULX in NGC 925 (ULX-3), detected in November 2017 by Chandra at a luminosity of L X = (7.8 ± 0.8) × 10 39 erg s −1 . Examination of archival data for NGC 925 reveals that ULX-3 was detected by Swift at a similarly high luminosity in 2011, as well as by XMM-Newton in January 2017 at a much lower luminosity of L X = (3.8 ± 0.5) × 10 38 erg s −1 . With an additional Chandra non-detection in 2005, this object demonstrates a high dynamic range of flux of factor 26. In its high-luminosity detections, ULX-3 exhibits a hard power-law spectrum with Γ = 1.6 ± 0.1, whereas the XMM-Newton detection is slightly softer, with Γ = 1.8 +0.2 −0.1 and also well-fitted with a broadened disc model. The long-term light curve is sparsely covered and could be consistent either with the propeller effect or with a large-amplitude superorbital period, both of which are seen in ULXs, in particular those with neutron star accretors. Further systematic monitoring of ULX-3 will allow us to determine the mechanism by which ULX-3 undergoes its extreme variability and to better understand the accretion processes of ULXs.

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“…As the thermal timescale mass transfer rate scales with the companion mass and inversely with the Kelvin Helmholz timescale (whilst its duration in this phase is dictated by the mass ratio), there is no obvious reason why the population of ULXs should not also contain stellar mass black holes (BHs). Indeed indirect arguments based around the nature of the accretion flow and geometrical beaming would support their presence in at least some systems (Middleton & King 2017) and binary population synthesis studies imply that BH ULXs may even dominate the observed population (Wicktorowicz et al 2018). However, determining the true relative proportion of neutron stars to black holes is extremely difficult as direct evidence of pulsations or CRSFs has been scant (e.g.…”

Section: Introductionmentioning

confidence: 99%

The Lense–Thirring timing-accretion plane for ULXs

Middleton

Fragile

Ingram

et al. 2019

Monthly Notices of the Royal Astronomical Society

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Identifying the compact object in ultraluminous X-ray sources (ULXs) has to-date required detection of pulsations or a cyclotron resonance scattering feature (CRSF), indicating a magnetised neutron star. However, pulsations are observed to be transient and it is plausible that accretion onto the neutron star may have suppressed the surface magnetic field such that pulsations and CRSFs will be entirely absent. We may therefore lack direct means to identify neutron star systems whilst we presently lack an effective means by which to identify black hole ULXs. Here we present a possible method for separating the ULX population by assuming the X-ray, mHz quasi-periodic oscillations (QPOs) and day timescale periods/QPOs are associated with Lense-Thirring precession of the inflow and outflowing wind respectively. The precession timescales combined with the temperature of the soft X-ray component produce planes where the accretor mass enters as a free parameter. Depending on the properties of the wind, use of these planes may be robust to a range in the angular momentum (spin) and, for high accretion rates, essentially independent of the neutron star's surface dipole field strength. Our model also predicts the mHz QPO frequency and magnitude of the phase-lag imprinted due to propagation through the optically thick wind; in the case of NGC 5408 X-1 we subsequently infer a black hole mass and high spin. Finally, we note that observing secular QPO evolution over sufficient baselines may indicate a neutron star, as the precession responds to spin-up which is not readily observable for black hole primaries.

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Predicting ultraluminous X-ray source demographics from geometrical beaming

Cited by 44 publications

References 26 publications

Evidence for Optically Thick, Eddington-limited Winds Driven by Supercritical Accretion

Evidence for Optically Thick, Eddington-limited Winds Driven by Supercritical Accretion

The (Re)appearance of NGC 925 ULX-3, a New Transient ULX

The Lense–Thirring timing-accretion plane for ULXs

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