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Modelling the spectral energy distribution of super-Eddington quasars

Kubota, Aya; Done, Chris

Modelling the spectral energy distribution of super-Eddington quasars Thumbnail


Aya Kubota


We develop a broadband spectral model, AGNSLIM, to describe super-Eddington black hole accretion disc spectra. This is based on the slim disc emissivity, where radial advection keeps the surface luminosity at the local Eddington limit, resulting in L(r)∝r−2 rather than the r−3 expected from the Novikov-Thorne (standard, sub-Eddington) disc emissivity. Wind losses should also be important but these are expected to produce a similar radiative emissivity. We assume that the flow is radially stratified, with an outer standard disc, an inner hot Comptonising region and an intermediate warm Comptonising region to produce the soft X-ray excess. This gives the model enough flexibility to fit the observed data, but with the additional requirement of energy conservation to give physical constraints. We use this to fit the broadband spectrum of one of the most extreme Active Galactic Nuclei, the Narrow Line Seyfert 1 RX J0439.6 − 5311, which has a black hole mass of (6 ∼ 9) × 106M⊙ as derived from the Hβ line width. This cannot be fit with the standard disc emissivity at this mass, as even zero spin models overproduce the observed luminosity. Instead, we show that the spectrum is well reproduced by the slim disc model, giving mass accretion rates around (5 ∼ 10) ×Eddington limit. There is no constraint on black hole spin as the efficiency is reduced by advection. Such extreme accretion rates should be characteristic of the first Quasars, and we demonstrate this by fitting to the spectrum of a recently discovered super-Eddington Quasar, PSO J006 + 39, at z = 6.6.


Kubota, A., & Done, C. (2019). Modelling the spectral energy distribution of super-Eddington quasars. Monthly Notices of the Royal Astronomical Society, 489(1), 524-533.

Journal Article Type Article
Acceptance Date Jul 30, 2019
Online Publication Date Aug 2, 2019
Publication Date Oct 30, 2019
Deposit Date Aug 7, 2019
Publicly Available Date Aug 7, 2019
Journal Monthly Notices of the Royal Astronomical Society
Print ISSN 0035-8711
Electronic ISSN 1365-2966
Publisher Royal Astronomical Society
Peer Reviewed Peer Reviewed
Volume 489
Issue 1
Pages 524-533


Accepted Journal Article (4.3 Mb)

Copyright Statement
This article has been accepted for publication in the Monthly notices of the Royal Astronomical Society ©: 2019 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.

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