The slimming effect of advection on black-hole accretion flows

Black hole mergers detectable with LIGO can occur in active galactic nucleus (AGN) disks. Here we parameterize the merger rates, the mass spectrum and the spin spectrum of black holes (BH) in AGN disks. The predicted merger rate spans ∼ 10 −4 − 10 4 Gpc −1 yr −1 , so upper limits from LIGO (< 212Gpc −1 yr −1 ) already constrain it. The predicted mass spectrum has the form of a broken power-law consisting of a pre-existing BH powerlaw mass spectrum and a harder powerlaw mass spectrum resulting from mergers. The predicted spin spectrum is multi-peaked with the evolution of retrograde spin BH in the gas disk playing a key role. We outline the large uncertainties in each of these LIGO observables for this channel and we discuss ways in which they can be constrained in the future.

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“…h/R ∼ 10 −3 -0.1 (Thompson et al 2005). h/R ∼ 0.1-0.7 in super-Eddington ADAFs (Lasota et al 2016). fg depends on h/R, ρ disk and τAGN .…”

Section: Rate Of Black Hole Binary Mergers In Agn Disksmentioning

confidence: 87%

Constraining Stellar-mass Black Hole Mergers in AGN Disks Detectable with LIGO

McKernan

Ford

Bellovary

et al. 2018

ApJ

284

224

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“…While the increased radiation pressure within the disk itself acts to increase its scale height, once this scale height is significant, radiation pressure from the opposite face of the funnel must also act against any further closing of its opening angle, which could potentially help produce this effect. Furthermore, Lasota et al (2016) argue that at the highest accretion rates the disk may become fully advectiondominated, and that in this regime the scale height of the disk can no longer increase (or equivalently, the opening angle of the inner funnel can no longer close) with increasing accretion rate, as basically all the energy is advected over the horizon and is not able to further inflate the disk. A roughly constant opening angle for the inner disk, as may be required to explain the broadband Holmberg IX X-1…”

Section: Discussionmentioning

confidence: 99%

The Broadband Spectral Variability of Holmberg IX X-1

Walton

Fürst

Harrison

et al. 2017

ApJ

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We present results from four new broadband X-ray observations of the extreme ultraluminous X-ray source Holmberg IX X-1 ( > L 10 X 40 erg s −1 ), performed by Suzaku and NuSTAR in coordination. Combined with the archival data, we now have broadband observations of this remarkable source from six separate epochs. Two of these new observations probe lower fluxes than seen previously, allowing us to extend our knowledge of the broadband spectral variability exhibited. The spectra are well fit by two thermal blackbody components thatdominate the emission below 10 keV, as well as a steep (G~3.5) power-law tail thatdominates above ∼15 keV. Remarkably, while the 0.3-10.0 keV flux varies by a factor of ∼3 between all these epochs, the 15-40 keV flux varies by only ∼20%. Although the spectral variability is strongest in the ∼1-10 keV band, both of the thermal components are required to vary when all epochs are considered. We also revisit the search for iron absorption features byleveraging the high-energy NuSTAR data to improve our sensitivity to extreme velocity outflows in light of the ultra-fast outflow recently detected in NGC 1313 X-1. Iron absorption from a similar outflow along our line of sight can be ruled out in this case. We discuss these results in the context of superEddington accretion models that invoke a funnel-like geometry for the inner flow, and propose a scenario in which we have an almost face-on view of a funnel that expands to larger radii with increasing flux, resulting in an increasing degree of geometrical collimation for the emission from intermediate-temperature regions.

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“…King 2008;Middleton et al 2015a). However, while this must happen over some range ofṀ in order for the disc structure to transition from the thin disc expected for standard sub-Eddington accretion to the funnel-like geometry expected for super-Eddington accretion, as discussed by Lasota et al (2016), once the disc reaches the point of being fully advection-dominated the opening angle of the disc should tend to a constant (H/R ∼ 1, where H is the scale height of the disc at radius R). Walton et al (2017) speculated that once this occurs, rather than closing the funnel further, an increase inṀ instead simply increases the characteristic radius within which geometric beaming occurs, such that emission that is already within this region (the highest energies probed) experiences no further collimation with an increase inṀ, while emission from larger radii (i.e.…”

Section: Modelmentioning

confidence: 99%

The unusual broad-band X-ray spectral variability of NGC 1313 X-1 seen with XMM–Newton, Chandra, and NuSTAR

Walton

Pinto

Nowak

et al. 2020

Monthly Notices of the Royal Astronomical Society

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We present results from the major coordinated X-ray observing programme on the ULX NGC 1313 X-1 performed in 2017, combining XMM–Newton, Chandra, and NuSTAR, focusing on the evolution of the broad-band (∼0.3–30.0 keV) continuum emission. Clear and unusual spectral variability is observed, but this is markedly suppressed above ∼10–15 keV, qualitatively similar to the ULX Holmberg IX X-1. We model the multi-epoch data with two-component accretion disc models designed to approximate super-Eddington accretion, allowing for both a black hole and a neutron star accretor. With regards to the hotter disc component, the data trace out two distinct tracks in the luminosity–temperature plane, with larger emitting radii and lower temperatures seen at higher observed fluxes. Despite this apparent anticorrelation, each of these tracks individually shows a positive luminosity–temperature relation. Both are broadly consistent with L ∝ T4, as expected for blackbody emission with a constant area, and also with L ∝ T2, as may be expected for an advection-dominated disc around a black hole. We consider a variety of possibilities for this unusual behaviour. Scenarios in which the innermost flow is suddenly blocked from view by outer regions of the super-Eddington disc/wind can explain the luminosity–temperature behaviour, but are difficult to reconcile with the lack of strong variability at higher energies, assuming this emission arises from the most compact regions. Instead, we may be seeing evidence for further radial stratification of the accretion flow than is included in the simple models considered, with a combination of winds and advection resulting in the suppressed high-energy variability.

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The slimming effect of advection on black-hole accretion flows

Cited by 49 publications

References 60 publications

Constraining Stellar-mass Black Hole Mergers in AGN Disks Detectable with LIGO

Constraining Stellar-mass Black Hole Mergers in AGN Disks Detectable with LIGO

The Broadband Spectral Variability of Holmberg IX X-1

The unusual broad-band X-ray spectral variability of NGC 1313 X-1 seen with XMM–Newton, Chandra, and NuSTAR

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