Radiation Hydrodynamic simulations of super-Eddington Accretion Flows

1. Radiation Hydrodynamic simulations of super-Eddington Accretion Flows  ①Super-Eddington accretion flows with photon-trapping (Ohsuga et al. 2005, ApJ, 628, 368) ②Limit-cycle oscillations driven by disk instability (Ohsuga 2006, ApJ, 640, 923) Ken OHSUGA Rikkyo University, Japan

2. 1. Super-Eddington Accretion Flows • Super-Eddington disk accretion flows • The super-Eddington disk accretion (Mdot > LE/c2 ; LE:Eddington luminosity) is one of the important physics for formation of the SMBHs. • The super-Eddington accretion might be an engine of the high L/LE objects, ULXs, GRBs, NLS1s, …. . • Mass outflow and radiation of the super-Eddington accretion flow are thought to affect the evolution of the host galaxies. • To understand the super-Eddington accretion is very important ! • In the super-Eddington accretion, the radiation pressure affects the dynamics of the flow. Multi-dimensional effects are important.

3. Radiation Energy Outflow Gas BH Viscous Heating Accretion Disk Photon-Trapping Photons fall onto BH with accreting gas We investigate the super-Eddington disk accretion flows by performing the 2D Radiation Hydrodynamic simulations. *Slim disk model (1D) cannot correctly treat the multi-dimensional effects

4. Basic Equations of Radiation Hydrodynamics Continuity Equation・・・・・・・ Radiation Force Equation of Motion・・・・・・・ Viscosity Gas Energy Equation・・・・・・ Radiation Energy Equation・・ Radiative Flux Absorption/Emission • Equation of State: p=(1)e, =5/3 • Radiation fields (F0, P0)： FLD approximation • -viscosity： P (=0.1, P:total pressure) • Absorption coefficient(=ff+bf), ff: free-free absorption, • bf:bound-free absorption (Hayashi, Hoshi, Sugimoto 1962)

5. Numerical Method • Explicit-implicit finite difference scheme on Eulerian grid (Spherical coordinates : 96 x 96 mesh) • Axisymmetry with respect to the rotation axis • Size of computational domain: 500rs • Initial condition: atmosphere (no disk) • Free outer boundary & absorbing inner boundary • Matter (0.45 x Keplerian angular momentum) is continuously injected into the computational domain from the outer disk boundary. • Parallel computing with PC cluster 500 z/rs Injection 500 BH r/rs

6. Gas Density Radiation Energy Density The quasi-steady structure of the super-Eddington accretion flows is obtained by our simulations.

7. Quasi-steady Structure Density & Velocity fields Ohsuga et al. 2005, ApJ, 628, 368 KH instability Bubbles & Circular Motion Outflow Mass-Accretion Rate Mass-accretion rate decreases near the BH. z/rs BH r/rs

8. Quasi-steady Structure Radiation Energy Density Radiation Pressure Gas Pressure Radiation Pressure-dominated Disk Gas Temperature Radiation Pressure-driven wind High Temperature Outflow/Corona Low Temperature Disk Radial Velocity Escape Velocity

9. Photon-Trapping Transport of Radiation Energy in r-direction z/rs Viscous Heating Radiation Luminosity[L/LE] Kinetic (Outflow) 2D RHD simulations BH r/rs Mass-accretion rate Radiation energy is transported towards the black hole with accreting gas (photon-trapping). We verify that the mass-accretion rate considerably exceeds the Eddington rate and the luminosity exceeds LE.

10.  BH Viewing-angle dependent Luminosity & Image Apparent Luminosity (Intrinsic Luminosity ~3.5LE ) Density Our simulations 4D2F()/LE Intensity Map [] The observed luminosity is sensitive to the viewing-angle. It is much larger than LE in the face-on view.

11. 2. Limit-Cycle Oscillations GRS1915+105 (micro quasar) 40s L~2LE L~0.3LE Janiuk & Czerny 2005 • Timescale of the luminosity variation is around 40s. • The disk luminosity oscillates between 2.0LE and 0.3LE(Yamaoka et al. 2001). • The intermittent JET is observed.

12. Disk instability in the radiation-pressure dominant region. If the mass-accretion rate from the disk boundary is around the Eddington rate, Mdot  LE/c2, the disk exhibits the periodic oscillations via the disk instability. Previous Topic (Mdot=103LE/c2 ) High state stable unstable This Topic (Mdot=102LE/c2 ) Mass-accretion rate stable Low state We investigate the time evolution of unstable disks by performing the 2D RHD simulations. Surface density

13. Super-Eddington state outflow Sub-Eddington state It is found that the disk structure changes periodically.

14. Mass accretion rate Outflow rate Trapped luminosity Luminosity Ohsuga 2006, ApJ, 640, 923 • The disk luminosity oscillates between 0.3LE and 2.0LE, and duration time is 30-50s. • Jet appears only in the high luminosity state. • These results are nicely fit to the observations of GRS 1915+105.

15. Conclusions(1) : super-Eddington accretion flow; Mdot >> LE/c2 • The mass accretion rate considerably exceeds the Eddington rate. The black hole can rapidly grow up due to disk accretion (Mdot/M~106yr). • The luminosity exceeds the Eddington luminosity. The apparent luminosity is more than 10 times larger than LE in the face-on view.  The luminosity of the ULXs can be understood by the super-Eddington accretion flow. • The thick disk forms and the complicated structure appears inside the disk. The radiation-pressure driven outflow is generated above the disk. • We found that the photon-trapping plays an important role. Conclusions(2) : limit cycle oscillations; Mdot  LE/c2 • The resulting variation amplitude (0.3LE⇔2.0LE) and duration (30-50s) nicely fit to the observations of microquasar, GRS 1915+105. • The intermittent jet is generated. • The physical mechanism, which causes the limit-cycle oscillations, is the disk instability in the radiation-pressure dominant region.