# Modelling the spectral energy distribution of super-Eddington quasars

## TL;DR

This paper introduces a broadband spectral model for super-Eddington quasars, successfully fitting observed spectra and revealing high accretion rates, with implications for early universe quasars.

## Contribution

The paper develops a new slim disc spectral model that accounts for super-Eddington accretion and fits observed spectra of extreme quasars, including high-redshift objects.

## Key findings

- The model accurately fits the spectrum of RX J0439.6-5311 with super-Eddington accretion rates.
- Standard disc models overpredict luminosity for the observed black hole mass.
- The model suggests early quasars likely experienced super-Eddington accretion phases.

## Abstract

We develop a broadband spectral model, agnsli}, 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) times 10^6 solar mass as derived from the H_beta 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) times 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.