Episodic Jets from Black Hole Accretion Disks

Shende, Mayur B.; Subramanian, Prasad; Sachdeva, Nishtha

doi:10.3847/1538-4357/ab1cb6

Cited by 10 publications

(9 citation statements)

References 61 publications

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“…Interestingly, such X-ray dips are thought to be related to episodic ejections in these sources, forming a blobby jet. Such episodic plasma ejections, which could be launched in a manner similar to solar coronal mass ejections (as envisaged by Shende et al 2019), have also been reported from GRS 1915+105 by for Comptonized X-rays. Our aim in this paper is to identify the collapse timescale of the inner accretion disc with the viscous infall timescale in this region.…”

Section: Introductionsupporting

confidence: 58%

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X-ray Dips in AGN and Microquasars -- Collapse Timescales of Inner Accretion Disc

Shende,

Chauhan,

Subramanian

2020

Preprint

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The temporal behaviour of X-rays from some AGN and microquasars is thought to arise from the rapid collapse of the hot, inner parts of their accretion discs. The collapse can occur over the radial infall timescale of the inner accretion disc. However, estimates of this timescale are hindered by a lack of knowledge of the operative viscosity in the collisionless plasma comprising the inner disc. We use published simulation results for cosmic ray diffusion through turbulent magnetic fields to arrive at a viscosity prescription appropriate to hot accretion discs. We construct simplified disc models using this viscosity prescription and estimate disc collapse timescales for 3C 120, 3C 111, and GRS 1915+105. The Shakura-Sunyaev α parameter resulting from our model ranges from 0.02 to 0.08. Our inner disc collapse timescale estimates agree well with those of the observed X-ray dips. We find that the collapse timescale is most sensitive to the outer radius of the hot accretion disc.

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Section: Introductionsupporting

confidence: 58%

“…The disc infall timescales (t infall ) obtained with this model are in good agreement with X-ray observations of 3C 120, 3C 111 and GRS 1915+105. Together with models such as Shende et al (2019), our work here outlines a plausible scenario for episodes of (inner) disc collapse accompanied by blob ejection.…”

Section: Discussionmentioning

confidence: 89%

X-ray Dips in AGN and Microquasars -- Collapse Timescales of Inner Accretion Disc

Shende,

Chauhan,

Subramanian

2020

Preprint

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“…A rather important aspect of the plasmoid-formation process that we have not yet discussed about is the presence of a considerable azimuthal motion in the plasmoids formed in our simulations. Hence, in addition to the intrinsic and background azimuthal motion of the accreting plasma (Shende et al 2019), plasmoids produced in 3D simulations can acquire an additional and considerable acceleration in the azimuthal direction when produced via reconnection. It is important to note here that plasmoids are significantly affected by the local guide field (Edmondson & Lynch 2017) and, indeed, episodic magnetic reconnection, such as break-out reconnection, has been observed in the solar corona (Kumar et al 2019).…”

Section: Plasmoids: Physical Conditions At Generationmentioning

confidence: 99%

Magnetic reconnection and plasmoid formation in three-dimensional accretion flows around black holes

Nathanail,

Mpisketzis,

Porth

et al. 2021

Preprint

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Magnetic reconnection is thought to be one of the main energy-dissipation mechanisms fueling energy to the plasma in the vicinity of a black hole. Indeed, plasmoids formed though magnetic reconnection may play a key role in γ-ray, X-ray and near-infrared flares from the black hole at the center of our galaxy, SgrA*. We report the results of three-dimensional general-relativistic ideal and resistive magnetohydrodynamics simulations modelling magnetic reconnection in accretion flows around astrophysical black holes. We show that current sheets are formed and destroyed rapidly in the turbulent environment of black-hole accretion. As this process operates, plasmoids are formed from the current sheets close to the event horizon and in a region of ∼ 2 −15 gravitational radii. We further quantify the magnetic dissipation and the process of energy transfer to the plasmoids, reporting the reconnection rate, the relative current density with respect to the local magnetic field, and the size of the plasmoids. We find that plasmoids gain energy through reconnection and heat up to relativistic temperatures, with the largest ones being sufficiently energetic to leave the black hole near the polar regions. During their evolution, plasmoids are stretched and elongated, becoming disrupted when the shear is sufficiently large, although some plasmoids survive as well-distinguished structures at distances of ∼ 30 − 40 gravitational radii from the black hole. Finally, we find that in some cases the plasmoids acquire a super-Keplerian azimuthal velocity, as suggested by recent observations of flares from Sgr A*.

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“…In addition to the nested-loops, different magnetic-field configurations have also been studied, leading to a picture in which jet launching is especially sensitive to the initial magnetic-field geometry (Beckwith, Hawley & Krolik 2008, 2009Barkov & Baushev 2011;Narayan et al 2012;Christie et al 2019b). More specifically, the outflows resulting from the accretion can vary depending on the initial magnetic-field configuration, going from jets that are weak and mostly turbulent, to powerful and collimated ones (Beckwith et al 2008;McKinney & Blandford 2009;Punsly, Igumenshchev & Hirose 2009;McKinney, Tchekhovskoy & Blandford 2012;Narayan et al 2012;Liska, Tchekhovskoy & Quataert 2018;Event Horizon Telescope Collaboration et al 2019;Shende, Subramanian & Sachdeva 2019;Vourellis et al 2019;White, Quataert & Gammie 2020). Although in the rather different context of the accretion on to the black hole produced as the result of a binary neutron-star merger, it was shown that intermittent jets can be produced when the disc is initially threaded by a purely toroidal magnetic field.…”

mentioning

confidence: 99%

Plasmoid formation in global GRMHD simulations and AGN flares

Nathanail

Fromm

Porth

et al. 2020

Monthly Notices of the Royal Astronomical Society

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One of the main dissipation processes acting on all scales in relativistic jets is thought to be governed by magnetic reconnection. Such dissipation processes have been studied in idealized environments, such as reconnection layers, which evolve in merging islands and lead to the production of ‘plasmoids’, ultimately resulting in efficient particle acceleration. In accretion flows on to black holes, reconnection layers can be developed and destroyed rapidly during the turbulent evolution of the flow. We present a series of two-dimensional general-relativistic magnetohydrodynamic simulations of tori accreting on to rotating black holes focusing our attention on the formation and evolution of current sheets. Initially, the tori are endowed with a poloidal magnetic field having a multiloop structure along the radial direction and with an alternating polarity. During reconnection processes, plasmoids and plasmoid chains are developed leading to a flaring activity and hence to a variable electromagnetic luminosity. We describe the methods developed to track automatically the plasmoids that are generated and ejected during the simulation, contrasting the behaviour of multiloop initial data with that encountered in typical simulations of accreting black holes having initial dipolar field composed of one loop only. Finally, we discuss the implications that our results have on the variability to be expected in accreting supermassive black holes.

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Episodic Jets from Black Hole Accretion Disks

Cited by 10 publications

References 61 publications

X-ray Dips in AGN and Microquasars -- Collapse Timescales of Inner Accretion Disc

X-ray Dips in AGN and Microquasars -- Collapse Timescales of Inner Accretion Disc

Magnetic reconnection and plasmoid formation in three-dimensional accretion flows around black holes

Plasmoid formation in global GRMHD simulations and AGN flares

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