Steady models of optically thin, magnetically supported black hole accretion disks

Hiroshi Oda, Mami Machida, Kenji E. Nakamura, Ryoji Matsumoto

Research output: Contribution to journalArticle

21 Citations (Scopus)

Abstract

We obtained steady solutions of optically thin, single-temperature, magnetized black hole accretion disks, assuming thermal bremsstrahlung cooling. Based on the results of 3D MHD simulations of accretion disks, we assumed that the magnetic fields inside the disk are turbulent and dominated by an azimuthal component. We decomposed the magnetic fields into an azimuthally averaged mean field and fluctuating fields. We also assumed that the azimuthally averaged Maxwell stress is proportional to the total pressure. The radial advection rate of the azimuthal magnetic flux, Φ̇, is prescribed as being proportional to ω, where ω is the radial coordinate and ζ is a parameter that parameterizes the radial variation of Φ̇. We found that when the accretion rate, Ṁ, exceeds the threshold for the onset of the thermal instability, a magnetic pressure-dominated new branch appears. Thus, the thermal-equilibrium curve of an optically thin disk has a 'Z'-shape in the plane of the surface density and temperature. This indicates that as the mass accretion rate increases, a gas pressure-dominated optically thin hot accretion disk undergoes a transition to a magnetic pressure dominated, optically thin cool disk. This disk corresponds to the X-ray hard, luminous disk in black hole candidates observed during the transition from a low/hard state to a high/soft state. We also obtained global steady transonic solutions containing such a transition layer.

Original languageEnglish
Pages (from-to)457-465
Number of pages9
JournalPublications of the Astronomical Society of Japan
Volume59
Issue number2
DOIs
Publication statusPublished - Jan 1 2007

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accretion disks
accretion
magnetic field
thermal instability
transition layers
transonic flow
advection
magnetic fields
bremsstrahlung
gas pressure
magnetic flux
temperature
cooling
thresholds
curves
gas
simulation
rate
x rays

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Steady models of optically thin, magnetically supported black hole accretion disks. / Oda, Hiroshi; Machida, Mami; Nakamura, Kenji E.; Matsumoto, Ryoji.

In: Publications of the Astronomical Society of Japan, Vol. 59, No. 2, 01.01.2007, p. 457-465.

Research output: Contribution to journalArticle

Oda, Hiroshi ; Machida, Mami ; Nakamura, Kenji E. ; Matsumoto, Ryoji. / Steady models of optically thin, magnetically supported black hole accretion disks. In: Publications of the Astronomical Society of Japan. 2007 ; Vol. 59, No. 2. pp. 457-465.
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