Ultraluminous X-ray sources as magnetically powered sub-Eddington advective accretion flows around stellar mass black holes

Abstract

In order to explain unusually high luminosity and spectral nature of ultra-luminous Xray sources (ULXs), some of the underlying black holes are argued to be of intermediate mass, between several tens to million solar masses. Indeed, there is a long standing question of missing mass of intermediate range of black holes. However, as some ULXs are argued to be neutron stars too, often their unusual high luminosity is argued by super-Eddington accretions. Nevertheless, all the models are based on non-magnetized or weakly magnetized accretion. There are, however, evidences that magnetic fields in accretion discs/flows around a stellar mass black hole could be million Gauss. Such a magnetically arrested accretion flow plausibly plays a key role to power many combined disc-jet/outflow systems. Here we show that flow energetics of a 2.5-dimensional advective magnetized accretion disc/outflow system around a stellar mass black hole are sufficient to explain power of ULXs in their hard states. Hence, they are neither expected to have intermediate mass black holes nor super-Eddington accretors. We suggest that at least some ULXs are magnetically powered sub-Eddington accretors around a stellar mass black hole.

FSRQ/BL Lac dichotomy as the magnetized advective accretion process around black holes: a unified classification of blazars

“…Unlike MAD, in our differentially rotating, quasi-spherical disc-outflow symbiosis, advection of both the toroidal and poloidal field is happening. Indeed, there is an upper limit to the amount of magnetic field what the disc around a BH can sustain, given by B E dd ≈ 10 4 G ( M 10 9 M ) −1/2 (Mondal & Mukhopadhyay, 2019). The required field strength to support our scenario is perfectly viable.…”

“…The magneto-centrifugally driven outflows from the disc threaded by large scale open magnetic field is a very efficient way to extract the gravitational potential energy of BH through accretion process. Also, the positive Bernoulli number in this highly magnetized advective flow provides a generic explanation of unbound matter and, hence, strong outflows (Mondal & Mukhopadhyay, 2019). Interestingly, the vertically inflated large toroidal fields create a magnetic pressure gradient, which further enhances an outward pressure to produce outflows and hence jets.…”

“…where F is the magnitude of the gravitational force for a BH in the pseudo-Newtonian framework (Mukhopadhyay, 2002). The set of equations without imposing vertical scaling was presented in Mondal & Mukhopadhyay (2019). The importance of generalized viscous shearing stress tensor (W i j ) is taking care explicitly in the present formalism.…”

Accretion into Black Hole, and Formation of Magnetically Arrested Accretion Disks

“…4, see [19]. Equation (52) does not change under a mirror transformation θ → π − θ and z → −z. So, the solution is anti-symmetrically extended to the lower hemisphere π/2 < θ ≤ π, with υ r having the same sign as at the upper hemisphere (directed to the centre,) and υ θ changes its sign (see Fig.4).…”

Slim Accretion Disks: Theory and Observational Consequences

“…Interesting possibility is related to the idea of Magneticall Arrested Disks (MAD) which could lead to modification of the flow close to the central object due to accumulated strength of the large-scale field lines. Such phenomenon has been considered by a number of authors [76,77], and it could be responsible for radio loud/radio quiet dychotomy in active galaxies, for the phenomenon of Changing Look (CL) AGN or for the appearance of Ultra-Luminous X-ray sources. However, simulations of MAD were generally done in the context of optically thin ADAF-type flow, and not in the case of slim disks, and we do not know if indeed the same mechanism can work also for those disks.…”