Magnetic flux stabilizing thin accretion disks

Abstract

We calculate the minimal amount of large-scale poloidal magnetic field that has to thread the inner, radiation-over-gas pressure dominated region of a thin disk for its thermal stability. Such a net field amplifies the magnetization of the saturated turbulent state and makes it locally stable. For a $10M_{\odot }$ black hole the minimal magnetic flux is $10^{24}(\dot{M}/{\dot{M}}_{\mathrm{Edd}}{)}^{20/21}\mathrm{G}\cdot \mathrm{c}{\mathrm{m}}^2$. This amount is compared with the amount of uniform magnetic flux that can be provided by the companion star -- estimated to be in the range $10^{22}-10^{24}\mathrm{G}\cdot \mathrm{c}{\mathrm{m}}^2$. If accretion rate is large enough, the companion is not able to provide the required amount and such a system, if still sub-Eddington, must be thermally unstable. The peculiar variability of GRS 1915+105, an X-ray binary with the exceptionally high BH mass and near-Eddington luminosity, may result from the shortage of large scale poloidal field of uniform polarity.

MNRAS Letters, in press

References in corpus (6)

• A Parallax Distance to the Microquasar GRS 1915+105 and a Revised Estimate of its Black Hole Mass
• Accretion Discs with Strong Toroidal Magnetic Fields
• The Origin of Black Hole Spin in Galactic Low-Mass X-ray Binaries
• Thermal stability of thin disk with magnetically driven winds
• The Cosmic Battery in Astrophysical Accretion Disks
• Discovery of GRS 1915+105 variability patterns in the Rapid Burster

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• On the efficiency of jet production in FR II radio galaxies and quasars
• Dynamical structure of highly eccentric discs with applications to tidal disruption events
• Jets in the soft state in Cyg X-3 caused by advection of the donor magnetic field and unification with low-mass X-ray binaries
• The Extreme Ultraviolet Variability of Quasars
• Importance of magnetic fields in highly eccentric discs with applications to tidal disruption events
• An Insight-HXMT view of the mHz quasi-regular modulation phenomenon in the black hole X-ray binary 4U 1630-47
• Recurrent Instability in LMXB Accretion Disks: How Strange is GRS 1915+105?
• Semi-Analytical Model for Wind-Fed Black Hole High-Mass X-ray Binaries -- State Transition Triggered by Magnetic Fields from the Companion Star --