Spectral models of convection-dominated accretion flows

Gregory H. Ball, Ramesh Narayan, Eliot Quataert

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56 Scopus citations


For small values of the dimensionless viscosity parameter, namely α ≲ 0.1, the dynamics of non-radiating accretion flows is dominated by convection; convection strongly suppresses the accretion of matter onto the central object and transports a luminosity ∼(10-3-10-2)Ṁc2 from small to large radii in the flow. A fraction of this convective luminosity is likely to be radiated at large radii via thermal bremsstrahlung emission. We show that this leads to a correlation between the frequency of maximal bremsstrahlung emission and the luminosity of the source, γpeak ∝ L2/3. Accreting black holes with X-ray luminosities 10-4 LEdd ≳ Lx(0.5-10 keV) ≳ 10-7 LEdd are expected to have hard X-ray spectra, with photon indices Γ ∼ 2, and sources with Lx ≲ 10-9LEdd are expected to have soft spectra, with Γ ∼ 3.5. This is testable with Chandra and XMM.

Original languageEnglish (US)
Pages (from-to)221-226
Number of pages6
JournalAstrophysical Journal
Issue number1 PART 1
StatePublished - May 1 2001
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Accretion, accretion disks
  • Black hole physics
  • Convection
  • X-rays: general


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