MHD Jets Around Galactic Objects

Casse, Fabien; Ferreira, Jonathan

doi:10.1007/978-94-010-0700-9_67

Cited by 9 publications

(16 citation statements)

References 4 publications

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“…This discrepancy in λ with our simulations could be explained by several aspects. If some additional heat is deposited at the base of the outflow, the disk ejection efficiency is enhanced which leads to the decrease of the magnetic lever arm (Casse & Ferreira 2000). Such heating could be a natural outcome of irradiation from the central object and local turbulent heating.…”

Section: Discussionmentioning

confidence: 99%

“…Irradiation from the central object or disk regions (as in Begelman et al 1983;Higginbottom & Proga 2015;Gressel et al 2020, for instance) could lead to a quantitative modification of our picture. Indeed, including heat deposition by external irradiation will probably lead to more massive outflows (Casse & Ferreira 2000) and modify the vertical stratification leading to the turbulent accreting layer. The study of such thermo-magnetic winds is postponed for future work.…”

Section: Discussionmentioning

confidence: 99%

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Magnetic outflows from turbulent accretion disks

Jacquemin-Ide

Lesur

Ferreira

2021

A&A

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Context. Astrophysical disks are likely embedded in an ambient vertical magnetic field generated by its environment. This ambient field is known to drive magneto-rotational turbulence in the disk bulk, but it is also responsible for launching magnetised outflows at the origin of astrophysical jets. Yet, the interplay between turbulence and outflows is not understood. In particular, the vertical structure and long-term (secular) evolution of such a system lack quantitative predictions. It is, nevertheless, this secular evolution which is proposed to explain time variability in many accreting systems such as FuOr, X-ray binaries, and novae like systems. Aims. We seek to constraint the structure and long-term evolution of turbulent astrophysical disks subject to magnetised outflows in the non-relativistic regime. More specifically we aim to characterise the mechanism driving accretion, the dynamics of the disk atmosphere, the role played by the outflow, and the long-term evolution of mass and magnetic flux distributions. Methods. We computed and analysed global 3D ideal magnetohydrynamic (MHD) simulations of an accretion disk threaded by a large-scale magnetic field. We measured the turbulent state of the system by Reynolds averaging the ideal MHD equations and evaluate the role of the turbulent terms in the equilibrium of the system. We then computed the transport of mass, angular momentum, and magnetic fields in the disk to characterise its secular evolution. Finally, we performed a parameter exploration survey in order to characterise how the transport properties depend on the disk properties. Results. We find that weakly magnetised disks drive jets that carry a small fraction of the disk angular momentum away. The mass-weighted accretion speed remains subsonic, although there is always an upper turbulent atmospheric region where transsonic accretion takes place. We show that this turbulence is driven by a strongly magnetised version of the magneto-rotational instability. The internal disk structure therefore appears drastically different from the conventional hydrostatic picture. We expect that the turbulent atmosphere region will lead to non-thermal features in the emission spectra from compact objects. In addition, we show that the disk is subject to a secular viscous-type instability, which leads to the formation of long-lived ring-like structures in the disk surface density distribution. This instability is likely connected to the magnetic field transport. Finally, we show that for all of the parameters explored, the ambient magnetic field is always dragged inward in the disk at a velocity which increases with the disk magnetisation. Beyond a threshold on the latter, the disk undergoes a profound radial readjustment. It leads to the formation of an inner accretion-ejection region with a supersonic mass-weighted accretion speed and where the magnetic field distribution becomes steady and reaches a magnitude near equipartition with the thermal pressure. This inner structure shares many properties with the jet emitting disk model. Overall, these results pave the way for quantitative self-consistent secular disk models.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Magnetic outflows from turbulent accretion disks

Jacquemin-Ide

Lesur

Ferreira

2021

A&A

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“…In contrast to commonly employed self-similar approaches (Casse & Ferreira 2000a;Jacquemin-Ide et al 2019) where stationary equations are solved with shooting methods through the critical points of the flow, here I solved the time-dependent Eqs. (1)-(3) using the code PLUTO, a finite-volume, shockcapturing scheme (Mignone et al 2007).…”

Section: Methodsmentioning

confidence: 99%

“…In this context, the purpose of this work is to take a step back and simplify the physics in order to explore the coupling between protoplanetary discs and magnetised winds in a more or less A&A 650, A35 (2021) systematic manner. This work essentially follows the approach initiated by Ferreira (1997) on globally self-similar models that was later extended to viscous (Casse & Ferreira 2000a) and weakly magnetised (Jacquemin-Ide et al 2019) discs. I use a relatively different technic to derive the wind solutions, however, which I present in the next section, along with the physical model.…”

Section: Introductionmentioning

confidence: 99%

Systematic description of wind-driven protoplanetary discs

Lesur

2021

A&A

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Aims. Planet-forming discs are believed to be very weakly turbulent in the regions outside of 1 AU. For this reason, it is now believed that magnetised winds could be the dominant mechanism driving accretion in these systems. However, currently, no self-consistent approach can describe discs that are subject to a magnetised wind in a way similar to the α disc model. In this article, I explore the parameter space of wind-driven protoplanetary discs in a systematic manner and present scaling laws that can be used in reduced models in a similar way to α disc models. Methods. I computed a series of self-similar wind solutions, assuming that the disc is dominated by ambipolar and Ohmic diffusion. These solution were obtained by searching for stationary solutions in the finite-volume code PLUTO using a relaxation method and continuation. Results. Self-similar solutions are obtained for values of plasma β ranging from 102 to 108 for several Ohmic and ambipolar diffusion strengths. Mass accretion rates of about 10−8 M⊙ yr−1 are obtained for the poloidal field strength β = O(104) or equivalently, 1 mG at 10 AU. In addition, the ejection efficiency is always close to 1, implying that wind mass-loss rate can be higher than the inner mass accretion rate when the wind-emitting region is large. The resulting magnetic lever arms are typically lower than 2, possibly reaching 1.5 in the weakest field cases. Remarkably, the mean transport properties (accretion rate and mass-loss rate) mostly depend on the field strength and much less on the disc diffusivities or surface density. The disc internal structure is nevertheless strongly affected by Ohmic resistivity, strongly resistive discs being subject to accretion at the surface while ambipolar only models lead to mid-plane accretion. Finally, I provide a complete set of scaling laws and semi-analytical wind solutions, which can be used to fit and interpret observations. Conclusions. Magnetised winds are unavoidable in protoplanetary discs as soon as they are embedded in an ambient poloidal magnetic field. Very detailed disc microphysics are not always needed to describe them, and simplified models such as self-similar solutions can capture most of the physics seen in full 3D simulations. The remaining difficulty to set up a complete theory of wind-driven accretion lies in the transport of the large-scale field, which remains poorly constrained and is not well understood.

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“…Irradiation of the outer disk by the inner X-ray emission seems the most natural process to link these two very distant regions on a very short timescale. Such radiative feedback of the inner regions on the outer disk wind properties is plausible, since the deposition of any additional power Q at the disk surface leads to the enhancement of mass loss, both in magneticallydriven (e.g., Casse & Ferreira 2000) and thermally-driven (e.g., Higginbottom & Proga 2015) outflows. The amount of X-ray luminosity incident on the disk at a radius r = R/R g in a ring of thickness ∆r depends on the exact geometry.…”

Section: Disk Irradiation As a Potential Driver Of The Change In The Disk Wind Properties During The Hard-to-soft Transitionmentioning

confidence: 99%

Expected evolution of disk wind properties along an X-ray binary outburst

Petrucci

Bianchi

Ponti

et al. 2021

A&A

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Blueshifted X-ray absorption lines (preferentially from Fe XXV and Fe XXVI present in the 6–8 keV range) indicating the presence of massive hot disk winds in black hole (BH) X-ray binaries (XrB) are most generally observed during soft states. It has been recently suggested that the nondetection of such hot wind signatures in hard states could be due to the thermal instability of the wind in the ionization domain consistent with Fe XXV and Fe XXVI. Studying the wind thermal stability does require, however, a very good knowledge of the spectral shape of the ionizing spectral energy distribution (SED). In this paper, we discuss the expected evolution of the disk wind properties during an entire outburst by using the RXTE observations of GX 339-4 during its 2010–2011 outburst. While GX 339-4 never showed signatures of a hot wind in the X-rays, the dataset used is optimal for the analysis shown in this study. We computed the corresponding stability curves of the wind using the SED obtained with the jet-emitting disk model. We show that the disk wind can transit from stable to unstable states for Fe XXV and Fe XXVI ions on a day timescale. While the absence of wind absorption features in hard states could be explained by this instability, their presence in soft states seems to require changes in the wind properties (e.g., density) during the spectral transitions between hard and soft states. We propose that these changes could be partly due to the variation of the heating power release at the accretion disk surface through irradiation by the central X-ray source. The evolution of the disk wind properties discussed in this paper could be confirmed through the daily monitoring of the spectral transition of a high-inclination BH XrB.

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MHD Jets Around Galactic Objects

Cited by 9 publications

References 4 publications

Magnetic outflows from turbulent accretion disks

Magnetic outflows from turbulent accretion disks

Systematic description of wind-driven protoplanetary discs

Expected evolution of disk wind properties along an X-ray binary outburst

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