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Radiatively Inefficient Accretion Flows

Radiatively Inefficient Accretion Flows. Roman Shcherbakov, 28 November, 2007. Radiative efficiency. Gas accretes onto the source, but does not radiate due to (1) low density (2) low electron temperature (3) large optical depth. efficiency

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Radiatively Inefficient Accretion Flows

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  1. Radiatively Inefficient Accretion Flows Roman Shcherbakov, 28 November, 2007

  2. Radiative efficiency Gas accretes onto the source, but does not radiate due to (1) low density (2) low electron temperature (3) large optical depth efficiency (function of gas density) Innermost Stable Circular Orbit (ISCO) Radiatively Inefficient Accretion Flows (RIAFs) Gas radiates away a lot of its grav. energy 0.06-0.42 efficiency (function of BH spin) ADAF

  3. The only realistic pattern: every astrophysical system has large angular momentum for a typical AGN for Sgr A* Possible RIAF configurations Spherical (Bondi) accretion + outflows – dimensionless angular momentum

  4. radius of influence of BH, 1pc for 10^8MSun – for Spherical accretion (Bondi, 1952) • u=cS at sonic radius rS, subsonic flow at r>rS, supersonic flow at r>rS • Such a solution is • Smooth • Has maximum accretion rate Efficiency Physical

  5. Thick disk accretion Adiabatic Inflow-Outflow Solution (Blandford, Begelman 1999) Hawley, Balbus 2002 Advection-Dominated Accretion Flow (Narayan, Yi 1995) Not only AGNs, but also Gamma Ray Bursts and protoplanetary disks

  6. ADAF luminosity Large optical depth ADAF (ULX sources) Narayan, Mahadevan, Quataert astro-ph/9803141

  7. ADAF/ADIOS/CDAF Advection-Dominated Accretion Flow (Narayan, Yi 1995) • Needed to fit the observations • Too low electron temperature Te<<Ti near the black hole • Too Low gas density near the black hole • Too small magnetic field in that region • ADAF is convectively unstable and does not include diffusion Adiabatic Inflow-Outflow Solution (Blandford, Begelman 1999) ADAF with outflows (Yuan 2001) Phenomenological inclusion of outflows “Thebinding energy of a gram of gas at a fewgravitational radii drives off 100 kg of gas from gravitational radii” – Blandford Convection-Dominated Accretion Flows (Narayan, Igumenshchev, & Abramowicz 2000) Accounts for convective instability of ADAF, but full 3-D analysis is not doable analytically

  8. Spectrum

  9. Jet-ADAF model for Sgr A* Yuan,Markoff, Falcke 2002

  10. Spectral states Soft – UV, IR Hard – X-Rays Narayan, Mahadevan, Quataert astro-ph/9803141 http://www.mpe.mpg.de/~amueller/lexdt_a02.html

  11. Hawley, Balbus, “The Dynamical Structure of Nonradiative Black Hole Accretion Flows” 2002, ApJ, 573, 738

  12. Hawley, Balbus, “The Dynamical Structure of Nonradiative Black Hole Accretion Flows” 2002, ApJ, 573, 738

  13. Results of Numerical Simulations Density Entropy Hawley, Balbus & Stone, 2001 ApJ, 554, L49

  14. Time variability Temperature At r=4rg Density

  15. Conclusions • Studies are controversial • Realistic accretion pattern is likely to be very complicated • Numerical simulations are preferable to analytical methods • Most effects are not yet included, small resolution • MHD instead of plasma calculations • Developed in the last 30 years, will we get the ultimate • answer within the next 30 years?

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