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General introduction Slim disk model (simplified model) Observational tests - Case of ULXs

Super-Critical Accretion? Shin Mineshige (Kyoto Univ.) with K. Ohsuga, K. Vierdayanti, K. Ebisawa, T. Kawaguchi TIARA Workshop (29/11/2006). General introduction Slim disk model (simplified model) Observational tests - Case of ULXs Multi-dimensional effects. 1. Introduction (background).

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General introduction Slim disk model (simplified model) Observational tests - Case of ULXs

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  1. Super-Critical Accretion?Shin Mineshige(Kyoto Univ.)with K.Ohsuga, K.Vierdayanti, K.Ebisawa, T.KawaguchiTIARA Workshop (29/11/2006) • General introduction • Slim disk model (simplified model) • Observational tests - Case of ULXs • Multi-dimensional effects

  2. 1. Introduction (background) There are some objects which seem to undergo super-critical (or super-Eddington) accretion. ・What are ULXs? What are NLS1s? ・What do we know from observations? ・What is key physics in super-critical accretion?

  3. IC342 galaxy UltraLuminousX-raysources(ULXs)Makishima et al. (2000), van der Karel (2003) • Bright (~1040ergs-1) compact X-ray sources • Successively found in off-center regions of nearby galaxies. • If L<LE, black hole mass should be > 100 Msun. LE~1038(M/Msun) erg s-1 • Two possibilities • Sub-critical accretion onto intermediate-mass BHs (M>100Msun). • Super-critical accretion onto stellar-mass BHs (M~3-30Msun).

  4. Do ULXs contain IMBHs?Miller et al. (2003, 2004) Arguments in favor of intermediate-mass BH (IMBH) • Luminosities sometimes exceed ~1040erg s-1(=LE of 100Msun) • Some ULXs showkT~0.1keV,indicating largeMBH(>100Msun) logLx highL & lowT =IMBHs(?) 1040erg/s 1037erg/s lowL & highT =stellar-massBHs 100Msun 10Msun logkT (keV) 0.1 keV1.0 keV

  5. Whatdeterminesdisktemperature? Energetics(Newtonian version) grav.energy:half→radiation energy half→rotation energy That is, (1/2)Egrav=Erad For r ~3rS, we have ⇒ BH 1keVfor10MsunBH, 0.1keVfor105MsunBH

  6. Narrow-lineSeyfert1galaxies(NLS1s) Boller et al. (NewA 44, 2000) • What are NLS1s? • Narrow “broad lines” (< 2000kms-1) • Seyfert 1 type X-ray features • Extremesoft excess & variability • Seem to contain less massive BHs • Good analogy with stellar-mass BHs in their very high (largeL) state. • High Tbb(∝MBH-1/4) ⇒ large soft excess • Small (GMBH/RBLR)1/2⇒ narrow line width • NLS1s = high L/LE system

  7. What is the Eddington luminosity? Spherical accretion system cannot shine at L>LE. accreting gas accreting gas radiation pressure Gravity>rad.pressure ⇒GM/r2 >κF/c ⇒L<LE=4πCGM/κ (∵F=L/4πr2)

  8. radiation pressure accreting gas accreting gas Diskaccretion may achieve L>LE Super-Eddington flux (F>LE/4πr2) is possible in the z-direction becauseofradiationanisotropy(!?) .

  9. . rtrap~ (Mc2/LE)rs What is Photon trapping? Begelman (1978), Ohsuga et al. (2002) When photon diffusion time,tdiff~Hτ/c, exceeds accretion time tacc~r/vr, photons are trapped. Low-energy photons Low-energy photons BH radiative diffusion & accretion High-energy photons trapped photons (c) K. Ohsuga

  10. 2. Slim disk model Slim disk model was proposed for describing high luminosity flows as an extension of the standard disk. ・What is distinct from the standard disk model? ・What are its observational signatures?

  11. L=LE log L/LE . . logm≡logM/(LE/c2) Slim disk modelAbramowicz et al. (1988); Watarai et al. (2000) • Basics This occurs within trapping radius rtrap~(Mc2/LE)rs • Model Radially 1-D model with radiation entropy advection • Spectrum τ≫ 1 → multicolor blackbody but with higher T accretion energy trapped photons .

  12. . M/(LE/c2)=1,10,102,103MBH=105Msun Slim-disk signatures1.smallinnermostradius 2.flatter temp. profile 3rS Slim-disk structureMineshige, Manmoto et al. (2002) Wang & Zhou (1999), Watarai & Fukue (1999) Low M rin～3rS ;Teff∝r-3/4 High M rin～rS;Teff∝r-1/2 . .

  13. What determines the inner edge ofadisk? Watarai & Mineshige (PASJ 55, 959, 2003) Classical argument: Circular orbits of a test particle become unstable atr<rms(=3rSfornospin BH) Case of slim disk: Usual stability analysiscannot apply because of no force balance. Same is true for ADAF. potential minimum slim-disk solutions The disk inner disk is not always at rin=rms.

  14. What determines temp. profile? Standard disk: Constant fraction of grav. energy is radiated away. Slim disk: Fraction of energy which is radiated away decreases inward: tdiff=tacc →Mc2/LE~r/rtrap∝r .

  15. Fν ν1/3 (smallr) hν ν-1 Fν (smallr) hν Spectral properties(e.g. Kato et al. 1998) Disk spectra = multi-color blackbody radiation Temperature profiles affect spectra T∝r-p ⇒ F∝ν3-(2/p) ・standard disk (p=3/4) ⇒F∝ν1/3 ・slim disk (p=1/2) ⇒F∝ν-1

  16. 3. Observational tests: Case of ULXs We examined the XMM/Newton data of several ULXs which were suggested to contain intermediate-mass black holes. ・How to test the theory? ・What did we find?

  17. Extended disk-blackbody model(Mitsuda et al. 1984; Mineshige et al. 1994) Fitting with superposition of blackbody (Bν) spectra: Fitting parameters: Tin= temp.of innermost region (～max.temp.) rin = size of the region emitting with Bν(Tin) p= temperature gradient Corrections: Real inner edge is at ～ ξrin with ξ～0.4 Higher color temp.; Tc=κTin with κ～1.7 ⇒ Good fits to the Galactic BBHs with p=0.75

  18. Spectralfitting1.Conventionalmodel(Roberts et al. 2005) Fitting with disk blackbody (p=0.75) + power-law We fit XMM-Newton data of several ULXs ⇒ lowTin～0.2keVandphoton index ofΓ=1.9 If we set rin~3rS, BH mass is MBH~300Msun. log conts NGC5204X-1 loghν

  19. Problem with DBB+PLfitting Spectral decomposition of DBB& PL components DBB comp. is entirely dominated byPL comp. Can we trust values derived from the minor component? log conts NGC5204X-1 loghν

  20. Spectralfitting2.ExtendedDBBmodel(Vierdayanti, SM, Ebisawa, Kawaguchi 2006) Model fitting, assuming T∝r-p We fit the same data but with the extended DBB model ⇒highTin~2.5keVandp=0.50±0.03(noPLcomp.) MBH~12Msun & L/LE~1, supporting slim disk model. log conts NGC5204X-1 loghν

  21. Why can both models give good fits? Because the spectral shapes are similar below ~10 keV. power-law (Γ=2) extended DBB with p=0.5 Both show fν∝ν-1 in 0.1~10keV range.

  22. The same test is needed for NLS1s Temperature-Luminosity diagram(Vierdayanti et al. 2006, PASJ 58, 915) Newmodelfitting gives MBH <30Msun. Low-temperature results should be re-examined!! logLx DBB + PL ext.DBB No evidence of IMBHs so far logkT (keV)

  23. ・ M (2) (1) Σ FateofPrad-driveninstability Radiation pressure-dominated SS disk is unstable. (1) relaxation oscillation? Honma et al. (1991), Szuszkiewicz & Miller (1998) (2) soft-to-hard transition? Takeuchi & Mineshige (1998), Gu & Lu (2000) (3) strongly clumped disk? Krolik (1998) (4) disk-corona structure? Nakamura & Osaki (1993), Svensson & Zdziarski (1994)

  24. Bursting behavior of micro-quasar(Yamaoka, Ueda & Inoue 2002) GRS 1915+105 exhibits state transitions between peak (slim disk) and valley (thin disk) counts time (T∝r-1/2 ) log Tin (T∝r-3/4 ) log rin

  25. 4. Multi-dimensional effects The slim-disk model applies only to the flow with L ~ LE. For even higher L, we need to perform radiation-hydrodynamical (RHD) simulations. ・What are the multi-dimensional effects? ・What can we understand them?

  26. A simple model(Ohsuga et al. 2002, ApJ 574, 315; 2003, ApJ 596, 429) Problem with the slim-disk formulation Radiative cooling rate is evaluated as ~ 4σT4/3τ (at same r) Consider a part of the disk which is moving inward Dynamics is given. Solve radiation transfer in z-direction. Can approximately evaluate 2D photon trapping effects. BH accretion radiative diffusion

  27. Photon trapping:observable effects Luminosity SED Variations Photon-trapping Slim disk MCD Slim disk Our results (Photon-trapping) 30 Luminosity[L/LE] Ohsuga et al. 2002 Ohsuga et al. 2003 Mass-accretion rate ・ ・ ・ m=10 m=100 m=10 • The slim-disk model overestimates the luminosity. • The frequency of the SED peak first increases then decreases with increase of mass-accretion rate. (c) K. Ohsuga

  28. 500 z/rs Injection 500 BH r/rs Our 2D RHD simulationsOhsuga, Mori, Nakamoto, SM (2005, ApJ 628, 368) • First simulations of super-critical accretion flows in quasi-steady regimes. • Matter with0.45KeplerianA.M. is continuously added through the outer boundary → disk-outflow structure • Flux-limited diffusion adopted. • αviscosity withα=0.1. • Mass input rate:1000(LE/c2) 　→luminosity of~3LE Initiallyemptydisk

  29. outflow z/rs disk flow BH r/rs density contours & velocity fields Overview of 2D super-critical flow Ohsuga et al. (2005, ApJ 628,368) Case of M=10Msun & M=1000LE/c2 ・ gas energy radiation energy density density (c) K. Ohsuga

  30. Why is accretion possible? Ohsuga & S.M. (2006, submitted) Radiation energy density is high;Erad ≫EE≡LE/4πr2c. Then why is the radiation pressure force so weak? Note radiation energy flux is Frad∝(κρ)-1∇Erad. → Because of highρand relatively flatEradprofile. Lowρand steepEradprofile yields super-Eddington flux.

  31. Photon trapping Fr=radiation flux in the rest frame F0r=radiation flux in the comoving frame Fr~F0r+vrE0 z/rs Photon trapping also helps reduced radiation pressure force. BH Radiation flux (Fr) is inward! r/rs (c) K. Ohsuga

  32. BH Density contours Significantradiationanisotropy Ohsuga et al. (2005, ApJ 628,368) luminosity 12 our simulations 4D2F()/LE 8 4 0 viewing angle The observed luminosity is sensitive to the viewing-angle; Maximum L ~ 12 LE!! ⇒ mild beaming (c) K. Ohsuga

  33. Why beaming? Heinzeller, S.M. & Ohsuga (2006, MNRAS 372, 1208,) Photon energy increases as θ decreases, why? - Because we see photons from deeper, hot region. - Because of Doppler effect. Why photon number increasesas θdecreases, why? - Because of anisotropic gas distribution. - Because Iν/ν3 is Lorentz invariant & hνincreases. gas gas radiation

  34. Future issueInteraction with magnetic fields Magnetic fields are essential ingredients in disks • Photon-bubble instability (Begelman 2002) • Magnetic tower jet → global RHD+MHD simulations necessary (Kato, SM, & Shibata 2004)

  35. Conclusions • Near- and super-critical accretion flows seem to occur in some systems (ULXs, NLS1s…?). • Slim disk model predicts flatter temperature profile. Spectral fitting with variable p proves the presence of supercritical accretion in ULXs. How about NLS1s? • 2DRHDsimulationsofsuper-criticalflowshowsuper- Eddingtonluminosity,significant radiation anisotropy (beaming), high-speed outflow, large absorption, etc. L can be ~10 LE!! • Issues:magneticfields, line spectra, instability,…

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