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Disk corona interaction: from X-ray binaries to AGN

Disk corona interaction: from X-ray binaries to AGN. Bifang Liu Yunnan Observatory, CAS. In collaboration with F. Meyer, E. Meyer-Hofmeister and S. Mineshige. Outline. The disk corona interaction: the evaporation process The disk corona evaporation model in X-ray binaries

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Disk corona interaction: from X-ray binaries to AGN

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  1. Disk corona interaction: from X-ray binaries to AGN Bifang Liu Yunnan Observatory, CAS In collaboration with F. Meyer, E. Meyer-Hofmeister and S. Mineshige

  2. Outline • The disk corona interaction: the evaporation process • The disk corona evaporation model in X-ray binaries • The magnetic reconnection-heated corona in AGN

  3. The disk corona evaporation model • First proposed by Meyer and Meyer-Hofmeister (1994) to interpret the UV delay in CVs • Developed to BHs by Meyer, Liu, Meyer-Hofmeister (2000) • Two-temperature model established by Liu, Mineshige, Meyer et al. (2002) • Other approaches in the same frame: • Rozanska & Czerny (2000), vertically approximated model • Dullemond (1999), semi-analytical model

  4. The disk corona interaction Meyer & Meyer-Hofmeister 1994 • Interaction of the disk and the corona: • Vertical heat conduction (Fc=-k0T5/2dT/dz) • mass evaporation • Steady accreting corona: Gas accretes to the BH, re-supplied by evaporating gas from the disk Conductive heat X-rays evaporation disk BH/NS/WD corona

  5. Vertical structure of the corona • Continuity equation • Momentum equation • Energy equation • Heat conduction (spitzer formula) • Equation of state • Boundary conditions (upper and lower) Coronal structure (P,T,ρ,vz) determined Evaporation rate: Means accretion flowing rate in the corona ．

  6. The radius-dependent evaporation rate Meyer, Liu, Meyer-Hofmeister,2000 • The maximal evaporation rate  0.02Eddington rate • The corresponding radius  300RS • Inclusion of magnetic field: maximal evaporation rate unchanged, corresponding radius shifted • Radial distribution of evaporation rate does not depend M 0.02 Influence of magnetic field . log mevap Qian, Liu, wu 2006 2.5 log r

  7. Complete depletion of the inner disk by evaporation • Condition for inner disk depletion • M<Mevap(max) • M>Mevap(max), disk extends to ISCO • M<Mevap(max), inner disk depleted • Truncation radius: Mevap(rtr)=M • • • • • • • • m=6

  8. Disk evaporation: two basic accretion modes

  9. Mass flow in the disk + corona Mass transferred from the companion star Mass flow in the outer cool disk . Accumulated in the outer disk Flow inwards:m . . m>mevap Evaporated into the corona Flow inwards through the disk Wind loss from the corona Accreted through the corona to BH Disk+corona ADAF

  10. Black hole X-ray binaries: observations Done et al 2004 Gilfanov et al 2000

  11. Transition of spectral states Well-known observational features • X-ray transients • Outburst: soft spectra • Quiescence: hard spectra • Persistent X-ray binaries Accretion rate varying up and down hard/soft spectral transition • Spectral transition occurs at L~1037ergs/s (~0.01Eddington rate) • • • •

  12. Interpreting the state transition • • Transition rate: • m>0.02, Disk-dominant accretion Soft spectral srtate • m<0.02, RIAF-dominant accretion Hard spectral state •

  13. Hysteresis in transition luminosity GX339-4 Observed light curve Schematic light curve of an X-ray nova outburst

  14. Explanation by disk corona model Meyer-Hofmeister, Liu, Meyer 2005 Different irradiation in hard and soft state leads to different evaporation rate and transition rate:

  15. Hysteresis caused by irradiations Liu, Meyer, Meyer-Hofmeister 2005 Accretion rates at hard/soft spectral transition for various irradiation from the central black hole Dependence of hysteresis on mean photon energy of irradiation

  16. Hysteresis in truncation radius

  17. The intermediate state Intermediate states occur during the decay of an outburst Liu, Meyer, Meyer-Hofmeister 2006 Accretion rate . log mevap Inner disk Corona Outer disk log r

  18. Spectral states of BHXBs Meyer, Liu, Meyer-Hofmeister 2006 Accretion rate decreases

  19. An inner disk below the ADAF Temperature distribution with height Vertical stratification of disk and corona

  20. Re-condensation from an ADAF into an inner disk Fraction of ADAF flow condenses onto an inner disk as a function of distance

  21. Summary: Disk corona model for X-ray binaries Provides a physical mechanism to explain • Truncation of the disk at low accretion rate • Spectral transition between hard and soft states • The hysteresis between the transitions of hard-to-soft and soft-to-hard states • Occurrence of intermediate state How about the disk corona in AGN?

  22. Observational similarities between AGN and BHXBs The fundamental plane for AGNs and BHXBs (Merloni et al. 2003) log LR=0.6log LX+0.78log M+7.33 Falcke et al. 2004: Proposed unification scheme

  23. Observational similarities between AGN and BHXBs Similarities in spectral states • Similarity between high-luminosity AGN and soft-state BHXBs (Maccarone et al. 2003) • Similarity between low-luminosity AGN and hard-state BHXBs (Narayan 2004; Falcke et al. 2004) • Similarity between NLS1s and very high state BHXBs? • Timescale in AGN much longer than in BHXBs Galactic sources: a laboratory for AGN?

  24. Disk corona model in AGN Theoretically, the disk corona mode does not depend on M. It predicts spectral transition rate 0.02 Eddington rate for AGN • Hard state: m<0.02 the Galactic Center, LLAGN, LINER, etc • Soft state: m>0.02 e.g. quasars, some of the Seyferts • An example of tentative spectral state transition Seyfert-LINER transition galaxy NGC7589 (Yuan, Komossa, Xu et al. 2005) Observations in AGN do show a critical accretion rate m0.02 (Maccarone et al 2003) · · ·

  25. Importance of corona in luminous AGN Luminous AGN and quasars (at soft state) • SED (optical-UV, soft and hard X-ray, broad fluorescent iron lines) indicates coexistence of hot gas and cold gas close to BH, which are usually thought to be the corona and thin disk. • The high X-ray luminosity means a large fraction of accretion energy released in the hot corona

  26. Problem in disk corona model for luminous AGN • The corona at high accretion rate is either over-cooled by inverse Compton scattering or blown away by radiation-driven winds. • Additional heating is required to keep the corona • The most promising heating mechanism: Magnetic field transports accretion energy to the corona, which is then released by magnetic reconnection

  27. The magnetic reconnection-heated corona Dynamo action in disk: Gravitational energy to B Liu, Mineshige, Shibata, 2002 Magnetic loops Magnetic loops emerge above the disk andreconnect in the corona Magnetic energy is transferred to thermal energy by reconnection Disk The heat is radiated to X-rays through Compton scattering reconnection

  28. The magnetic reconnection-heated corona Interactions between the disk and corona • Magnetic field transports accretion energy from the disk to the corona • Disk radiations are Compton scattered in the corona • Heat is conducted by electrons from corona to chromosphere • Evaporating gas supplies for the corona accretion

  29. The disk with corona above Shakura-Sunyaev (1973) disk • Disk quantities determined by M, M and energy fraction dissipated in the disk (1-f) Pd=Pd (M,M, f), Td =Td (M,M, f) • Equipartition between the magnetic energy and gas thermal energy in the disk: Pd=B2/8π B=B(M, M, f) • • • •

  30. The corona above a disk Energy balance reconnection heating = Compton coolingin corona conduction heating = evaporation cooling in chromosphere ⇒ T(M, M, f), n (M, M, f) • •

  31. Determination of energy fraction dissipated in corona • Equation concerning f for given M and M • • Solve the equation for f Calculate the disk variables Calculate the corona T, n, τ for given M and M •

  32. Two solutions for disk-corona model Gas pressure-dominated (disk) solution Exists for accretion rate>0.02 • Most of the accretion energy is transferred to the corona, f ~ 1 • Corona is strong withT～ 109 K, n～ 109 cm-3 and Compton radiation is large • Disk is cool with temperature T~ a few104K • Backward Compton radiation is reprocessed as seed soft photons, little intrinsic disk contribution

  33. Two solutions for disk-corona model Radiation pressure-dominated (disk) solution Exists for high accretion rate • Most of the accretion energy is dissipated in disk, f « 1 • Disk is like a usual one with temperature T~105—T~107K • Corona is weak withT ～ 108 K, n ～ 108 cm-3 and Compton radiation is low • The emission is dominated by disk multi-color blackbody emission

  34. Emission from disk and corona • Disk emission: multi-color blackbody • Emergent emissions—disk photons coming out of the corona • Part of them come out without scattering (disk component): Observed UV and soft X-rays • Part of them are Compton upscattered in corona • Coming out upwards: the observed X-rays • Going out backwards: processed as seed photons Spectra from Monte Carlo Simulations

  35. Spectra from disk+corona Two types of spectrum • Hard spectrum: Multi-color blackbody +Power law X-rays • Soft spectrum: Multi-color blackbody • Hard spectrum can occur for both high m and low m (m>0.02) • Soft spectrum occurs only for high m Liu, Mineshige, Ohsuga 2003 · · · ·

  36. Spectra emerging from the corona Hardspectrum: Power Law, α~ 1.1--1.2 (Γ ~ 2.1--2.2 ) Occurrence at accretion rate>0.02 Eddington rate Spectra similar to that of Haardt & Maraschi 1991,1993 M=108Msun L=0.7LEdd L=0.35LEdd L=0.07LEdd

  37. Spectra emerging from the corona Soft spectrum: Occurrence only in luminous system M=108Msun L=0.7LEdd

  38. What’s new in our model? • Propose a mechanism for transferring accretion energy to the corona • Establish a self-consistent disk+corona model • Interpret strong X-ray radiation in AGN • Interpret the very high state in BHXBs (the spetrem seems too flat)? Disk and corona variables and spectra are solely determined by m and mdot Modeling observations without free parameters

  39. Summary: B-heated corona Liu, Mineshige, Ohsuga 2003 • for a relatively low-luminosity system (<0.02<L/LEdd<0.2) Hard spectrum: Power law, ≈1.1 comparable with Seyfert galaxies:  ≈0.9-1.0 • for a high-luminosity system (L>0.2LEdd) either hard spectrum ≈1.1 or soft spectrum (disk dominated MCD) • BH mass independent, applicable to stellar-mass black hole

  40. Conclusion The disk corona interaction leads to • depletion of the inner disk at low accretion rate • Triggering the spectral state transition • Formation of a weak interior disk: the intermediate state • Hysteresis observed in X-ray binaries • Magnetic reconnection heated corona in AGN: the strong X-ray radiations • Magnetic reconnection heated corona in BHXBs: the very high state?

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