Coronal outflow dominated accretion discs: a new possibility for low-luminosity black holes?

By A. Merloni, A. C. Fabian. 2001

154 citations recorded by the source corpus.

The spectral-energy distributions of galactic black holes in the low/hard state and of low-luminosity active galactic nuclei (AGNs) possess many common features, the most prominent being: compact, flat- (or inverted-)spectrum radio cores with high brightness temperatures; excess red and infrared emission, often correlated with the radio flux; an extremely weak (or absent) quasi-thermal hump and a hard-X-ray power-law with high-energy cut-off. These sources are thought to be accreting at low rates, and advection- (or convection-)dominated accretion flows are usually considered the best candidates to explain them. Here we present an alternative possibility, involving strong, unbound, magnetic coronae generated by geometrically thin, optically thick accretion discs at low accretion rates. First we show that, if angular momentum transport in the disc is due to magnetic turbulent stresses, the magnetic energy density and effective viscous stresses inside the disc are proportional to the geometric mean of the total (gas plus radiation) and gas pressure. Therefore the corona is less powerful in a radiation-pressure dominated disc, and the relative fraction of the power liberated in the corona increases as the accretion rate decreases. Furthermore, we discuss why energetically dominant coronae are ideal sites for launching powerful jets/outflows, both MHD- and thermally driven. In analysing the spectral properties of such coronal-outflow dominated accretion discs, we reach the important conclusion that if the jet/outflow is, as is likely, radiatively inefficient, then so is the source overall, even without advection of energy into the black hole being relevant for the dynamics of the accretion flow.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/9b48fa067d7e2b23947f0a3567acebaafcc419ea

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Citations in the corpus

Radiatively efficient accreting black holes in the hard state: the case study of H1743-322 (2011, background): “…and geometrically thin accretion disc model (Shakura & Sunyaev 1973), some models of accretion disc coronae (ADC) (see e.g., Galeev, Rosner & Vaiana 1979; Haardt & Maraschi 1991; Di Matteo, Celotti & Fabian 1999; Merloni & Fabian 2002) or the luminous hot accretion flow model (LHAF Yuan 2001).”
ARE THE VARIATIONS IN QUASAR OPTICAL FLUX DRIVEN BY THERMAL FLUCTUATIONS? (2009, background): “If the stress is not proportional to the total pressure, but rather some other combination of the gas and radiation pressure, then the disk becomes more stable to thermal perturbations (e.g., Stella & Rosner 1984; Szuszkiewicz 1990; Merloni & Fabian 2002; Merloni 2003).”
Measuring the kinetic power of active galactic nuclei in the radio mode (2007, background): “As it was proposed by Merloni & Fabian (2002) and discussed also in Kuncic& Bicknell (2007), strong magnetic field threading a thin discmay remove energy and angular momentum (and very little mass) without radiating efficiently, and in so doing generating powerful,Poynting dominated outflows.”
On the origin of radio emission in radio-quiet quasars (2008, background): “X relation in GBHs and in AGN is that it results from a disc/jet coupling (e.g. Merloni et al. 2003; Falcke et al. 2004) or more specifically from a corona/jet coupling, as the corona feeds the base of the jet (e.g. Merloni & Fabian 2002; Markoff, Nowak & Wilms 2005).”
A universal radio-X-ray correlation in low/hard state black hole binaries (2003, background): “…all the evidence points to the corona in these sys- tems being physically related to the presence of a jet: by far the simplest interpretation therefore is that the Comptonising region is just the base of the relativistic outflow (Fender et al. 1999b; Merloni & Fabian 2002; Markoff et al. 2003a).”
A radio-emitting outflow in the quiescent state of A0620−00: implications for modelling low-luminosity black hole binaries (2006, background): “Another possible scenario for low-luminosity BHs is that proposed by Merloni & Fabian (2002), where strong, unbound, magnetic coronae are powered by thin discs, with the relative fraction of the power liberated in the corona increasing as the accretion rate decreases.”
Neutrino Trapping and Accretion Models for Gamma-Ray Bursts (2002, background): “Bpd is the poloidal field in the disk given, approximately, by Bpd ∼ (H/R)B (see also Merloni & Fabian 2002).”
A Unified Model for Black Hole X-Ray Binary Jets? (2004, background): “…within thin discs, as is the basis ofthe BP mechanism, but rather in a geometrically thick flow (see alsoe.g. Blandford & Begelman 1999; Meier 2001; Merloni & Fabian 2002) As the accretion rate increases the power of this disc-jet will increase and the geometrically thin accretion disc will…”
Hot Accretion Flows Around Black Holes (2014, background): “One way out is to postulate that the corona forms the base of an outward-moving jet (Beloborodov 1999, Malzac et al. 2001, Merloni & Fabian 2002).”
The Dynamical Structure of Nonradiative Black Hole Accretion Flows (2002, background): “The observational evidence for coronal outflows in low-luminosity black hole sources has been recently emphasized by Merloni & Fabian (2002).”
A Fundamental plane of black hole activity (2003, background): “Merloni & Fabian (2002) and Merloni (2003) have shown how it is possible to derive coupled equations for the accretiondisc– corona systems under very simple assumptions about the nature of the turbulent magnetic viscosity inside the disc.”
Correlations between X-ray and radio spectral properties of accreting black holes (2002, methodology): “Within the framework of this model, radio emission may arise from the jet being formed by the coronal outflow (Merloni & Fabian 2002).”
Long term variability of Cygnus X-1. I. X-ray spectral-temporal correlations in the hard state (2002, background): “…threshold rate such as the magnetorotational instability (Balbus & Hawley 1991), advection (Esin et al. 1997), or some kind of coronal outflow (Merloni & Fabian 2002; Blandford & Begelman 1999, and references therein), while others have claimed the presence of an up to now unknown additional…”
Black hole accretion discs in the canonical low‐hard state (2009, background): “…law comes from either a patchy corona, possibly powered by magnetic flares (Beloborodov 1999; Di Matteo, Celotti & Fabian 1999; Merloni, Di Matteo & Fabian 2000; Merloni & Fabian 2001) or the base of a centrally located jet (Merloni & Fabian 2002; Markoff & Nowak 2004; Markoff, Nowak & Wilms 2005).”
Nuclear Activity in Nearby Galaxies (2008, background): “Finally, Merloni & Fabian (2002) proposed that LLAGNs do contain a cold thin disk, but because of their low mass accretion rates, they liberate a large fraction of their gravitational energy in a strongly magnetized, unbound corona.”