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吸积盘的蒸发与冕

吸积盘的蒸发与冕. 引言： 吸积的重要性 黑洞 X- 射线双星中的观测光谱 基本的吸积理论模型 吸积盘与冕：从 CV 到 X-ray 双星 光谱态变换中的延迟现象：吸积盘与冕模型的另一观测支持 AGN 中的吸积盘与冕：磁重联模型. 吸积的重要性. 几乎所有天体中都存在不同程度的吸积 亮天体辐射的主要能量来源 不同的吸积过程形成不同类型的天体。 研究吸积是了解宇宙物理本质至关重要的途径。. 吸积的观测事实. Gilfanov et al 2000. Cyg X-1 的光谱态变化.

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吸积盘的蒸发与冕

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  1. 吸积盘的蒸发与冕 • 引言： • 吸积的重要性 • 黑洞X-射线双星中的观测光谱 • 基本的吸积理论模型 • 吸积盘与冕：从CV到X-ray双星 • 光谱态变换中的延迟现象：吸积盘与冕模型的另一观测支持 • AGN中的吸积盘与冕：磁重联模型

  2. 吸积的重要性 • 几乎所有天体中都存在不同程度的吸积 • 亮天体辐射的主要能量来源 • 不同的吸积过程形成不同类型的天体。 研究吸积是了解宇宙物理本质至关重要的途径。

  3. 吸积的观测事实 Gilfanov et al 2000 Cyg X-1的光谱态变化

  4. Soft- and hard-state black hole binaries High/soft state Low/hard state McClintock 2005

  5. Two basic spectral states soft logfν hard log hν hard (low) state power-law,fν ∝ν-α with α～0.7 cutoff at ～100keV soft (high) state blackbody spec. withkT～1keV

  6. Basic Accretion Models The presence of two (basic) spectral states indicates two different modes of accretion • Standard accretion disk • Advection-Dominated Accretion Flow (ADAF)

  7. The difference between standard disk and ADAF Energy equation:Accretion =Radiation + Advection • Standard disk: • ADAF Accretion Energy Radiation • Cool, bright, Geometrically thin disk ≫ 1: multi-color blackbody  Soft state spectra Accretion Energy Internal thermal energy (Advection) • Hot, Faint, Geometrically thick accretion flow < 1: Syn. Brem, Comp.  Hard state spectra

  8. Multi-colour Blackbody spectra (optically thick) kT ~1 keV ( BH binaries) kT ~ 10 eV (AGN) Spectrum from disk Shakura & Sunyaev 1973 Log n f(n) Log n

  9. Spectrum from ADAF Narayan et al. 1998

  10. Narayan et al. 1998 M=10MSun Disk M=10MSun ADAF M=109MSun ADAF M=109MSun Disk

  11. 为什么要研究吸积盘的冕？ 冕的概念：高温、稀薄气体 日冕：106K, 吸积盘冕107-109K 吸积盘冕 日冕

  12. 观测光谱的多样性与复杂性 • Observations show that the accretion process in individual objects is far more complicated than the two basic accretion modes, indicating • Inner ADAF+ outer disk • Corona above/underneath disk Done et al. 2004

  13. 经典吸积盘与冕的蒸发模型 Meyer & Meyer-Hofmeister 1994 • Large dT/dz • Mass and energy exchange • Originally aims to solve UV delay in DN outbursts X-rays evaporation disk BH/NS/WD Conductive heat corona

  14. Accretion disk corona • Continuity equation • Momentum equation • Energy equation • Equation of state • Viscosity law • Boundary conditions Structure of the disk corona and evaporation rate . Log M Log R 重要结果：距白矮星越近，吸积盘的蒸发越强

  15. Disk evolution with evaporation in DNe A B Log  Evolution of disk surface density Σ(r) with time (in days) during quiescence

  16. Consequence of evaporation in DNe Formation of coronal “hole” during quiescence UV delay during the rise of outburst

  17. Disk evolution with evaporation in WZ-sge type DNe and XNe Evaporation prevents early triggering of an outburst Extremely long recurrence time

  18. 黑洞系统中的吸积盘和冕 黑洞附近的吸积盘和冕 • Coronal flow along distance • Outer region (r >103rg): • weak coronal flow • Middle region (r~340rg): efficient evaporation, strong corona • Inner region (r<340rg ): • no much evaporation 吸积盘蒸发率及冕的温度分布随黑洞距离的分布. （M=6Msun)

  19. Transition of accretion mode 吸积形式取决于吸积率 • For Mdot>Mdotcrit, disk dominant • For Mdot<Mdotcrit, corona dominant 临界吸积率 Transition of spectrum in dependence on the accretion rate

  20. Two basic spectral states Schematic view of accretion in hard and soft state

  21. Transition of spectrum • X-ray transients • Outburst: Mdot>Mdotcrit, soft state • quiescence: Mdot<Mdotcrit, hard state • Persistant X-ray binaries (e.g.Cyg X-1) Mdot varying up and down hard/soft spectral transition Change occurs at L~1037ergs/s (Mdot~1017g/s)

  22. Change from outer thin disk to inner corona/ADAF What causes the change of accretion mode and how to determine rtr? Narayan et al (1998) Done et al. 2004

  23. What causes the change of accretion mode? 热冕 基本思想：盘内区的强蒸发耗空内盘，从而使吸积由外区薄盘主导过渡到内区ADAF主导，转换半径由黑洞质量与吸积率决定。 . Log m 冷盘 黑洞 ADAF ADAF+Disk+Corona Log r

  24. Accretion flows around BH • ADAF/CDAF: Very low-mdotsystem e.g. Quiescent BHCs • Inner ADAF+Outer disk+corona:Low mdot • Standard disk+corona: Medium/high mdot • Slim disk (+corona？): Very high-mdot system

  25. Hysteresis in X-ray binaries--Additional support to the disk evaporation model Schematic light curve of an X-ray nova outburst

  26. Model explanation Different irradiation in hard and soft state leads to different evaporation rate and transition rate Compton cooling

  27. AGN中的吸积 Observational features in AGN • SED: power-law • Radio: synchrotron • IR: warm dust grain • BBB: disk • Soft x-ray excess+ hard X-ray tail: disk+comptonization+Bremsstrahlung • 6.4keV fluorescent iron lines: reflection of hard X-rays • SED indicates hot plasma + cold gas, which is commonly thought to be corona+thin disk

  28. Theoretical disk+corona model in AGNs • 盘与冕特征：AGN盘辐射强，导致很强的逆Compton散射 冕物质被冷却凝聚到盘，黑洞附近冕不存在。 与观测相矛盾！ • 问题：是什么供给冕能源以维持它的存在？ 以往的冕模型简单地假设通过吸积所释放的引力能全部或绝大部分都在冕中释放 (e.g. Haardt & Maraschi 1991; Nakamura & Osaki 1993; Kawaguchi, Shimura, & Mineshige 2001)。

  29. Magnetic fields in Accretion Flow Role of magnetic fields • Source of viscosity • Cause of flares, producing variability • Source of radiation (via synchrotron) • Jet & outflow formation • Disk corona heating

  30. 吸积盘与冕的磁重联模型 • 基本思想：中心天体（黑洞）吸积周围物质在盘中所释放的引力能以磁能的形式存储于磁环中，通过Parker不稳定性磁环上浮到冕中，在那里通过磁重联转换成热能，进而由Compton散射产生X-ray 辐射。 • 解决AGN中冕辐射的能源短缺问题

  31. Accretion energy to radiation Dynamo action in disk: Gravitational energy to B Magnetic loops Magnetic loops emerge above the disk and reconnect in the corona Disk Magnetic energy is transferred to thermal energy reconnection The heat is radiated to X-rays through Compton scattering

  32. Two solutions for disk-corona model Gas pressure-dominated (disk) solution Exists for both high and low mdot • 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 only for high mdot • 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. Spectra from disk+corona Two spectral states found by Monte Carlo simulations • Hard state: Multi-color blackbody +Power law X-rays • Soft state: Multi-color blackbody • Hard state can occur for both high mdot and low mdot • Soft state occurs only for high mdot

  35. Spectra emerging from the corona Hard-state spectrum: Power Law, α~ 1.1--1.2 (Γ ~ 2.1--2.2 ) Occur in either low- or high-luminosity system M=108Msun L=0.7LEdd L=0.07LEdd

  36. Spectra emerging from the corona Soft-state spectrum: Occur only in luminous system M=108Msun L=0.7LEdd

  37. 吸积盘与冕磁重联模型小结 • for a low-luminosity system (L<0.2LEdd) Hard spectrum: Power law, ≈1.1 In Seyfert galaxies:  ≈0.9-1.0(扣除反射成分后） • for a high-luminosity system (L>0.2LEdd) either hard spectrum ≈1.1 or soft spectrum (disk dominated MCD) • Mass independent, applicable to stellar-mass black hole

  38. Spectral transition:from low to very high state Possible mechanism? L/LEdd Spectral state Accretion flow Slim disk ~1. Pg disk, B strong, Evaporation efficient Very high Disk+strong corona ~0.2 Pr disk, B small, Evaporation inefficient High/soft Disk+weak corona ~0.02 Evaporation depletes the inner disk, Rin(mdot), Little B(?) Low/hard ADAF+disk

  39. Summary Accretion disk and corona • CVs: UV delay in DNe, long recurrence in WZ-Sge type DNe and XNe • X-ray transients: quiescent and outburst states • BH X-ray binaries: Continuously change of spectral state • AGNs: Magnetic reconnection heated corona+disk

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