Magnetized advective accretion flows: formation of magnetic barriers in magnetically arrested discs

Abstract

We discuss the importance of large scale strong magnetic field in the removal of angular momentum outward, as well as the possible origin of different kinds of magnetic barrier in advective, geometrically thick, sub-Keplerian accretion flows around black holes. The origin of this large scale strong magnetic field near the event horizon is due to the advection of the magnetic flux by the accreting gas from the environment, say, the interstellar medium or a companion star, because of flux freezing. In this simplest vertically averaged, 1.5−dimensional disc model, we choose the maximum upper limit of the magnetic field, which the disc around a black hole can sustain. In this so called magnetically arrested disc (MAD) model, the accreting gas either decelerates or faces the magnetic barrier near the event horizon by the accumulated magnetic field depending on the geometry. The magnetic barrier may knock the matter to infinity. We suggest that these types of flow are the building block to produce jets and outflows in the accreting system. We also find that in some cases, when matter is trying to go back to infinity after knocking the barrier, matter is prevented being escaped by the cumulative action of strong gravity and the magnetic tension, hence by another barrier. In this way, magnetic field can lock the matter in between these two barriers and it might be a possible explanation for the formation of episodic jet.

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

“…The event horizon where the matter velocity reaches the light speed provides the inner boundary. To capture the sonic/critical point conditions, we combine the above fundamental model equations appropriately (see, e.g., Rajesh & Mukhopadhyay 2010;Mondal & Mukhopadhyay 2018, for detailed description). At the critical radius r c , we need to specify the electron temperature T ec and specific angular momentum λ c .…”

“…We initiated the role of large scale magnetic field in a 1.5dimensional advective accretion flow, emphasizing that the presence of strong field could change the disc flow behaviors drastically in the vicinity of BH event horizon (Mondal & Mukhopadhyay, 2018). Here, we consider a magnetized, viscous, 2.5-dimensional, advective disc-outflow/jet symbiotic model in a more complete framework by taking care of cooling mechanisms explicitly as discussed in Section 2.…”

Episodic Jets from Black Hole Accretion Disks

“…We adopt the latter scenario. Some models addressing the origin of such episodic emission appeal to instabilities or similar interruptions to the steady-state description of the accretion-ejection phenomenon (e.g., Stepanovs et al 2014;Mondal & Mukhopadhyay 2018;Chakrabarti et al 2002;Garain et al 2019). Giannios et al (2009) argue that spontaneous reconnection episodes in a Poynting flux dominated jet can produce small-scale jets (equivalently, small blobs of plasma) and Mizuta et al (2018) employ GRMHD simulations to suggest that the episodic variations in the accretion rate can produce intense Alfvénic pulses.…”

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

“…We consider here the flows passing through the soundvelocity point and supersonic near the centre of gravity. In presence of a magnetic field more singular points may appear in the accretion flow, connected with magneto-sonic and Alfven velocities, see [29,51]. In our consideration the transition through the gas sonic point happens far from BH and equipartition zone, where magnetic field influence may be neglected.…”