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Black Hole Binaries

Black Hole Binaries. Chapter 4 in Compact Stellar X-ray Sources eds. W.H.G. Lewin and M. van der Klis, Cambridge University Press, astro-ph/0306213. Jeffrey E. McClintock (CfA) & Ronald A. Remillard (MIT). Hua Feng, THCA journal club. Outline. Introduction

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Black Hole Binaries

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  1. Black Hole Binaries Chapter 4 in Compact Stellar X-ray Sources eds. W.H.G. Lewin and M. van der Klis, Cambridge University Press, astro-ph/0306213 Jeffrey E. McClintock (CfA) & Ronald A. Remillard (MIT) Hua Feng, THCA journal club

  2. Outline • Introduction • X-ray light curves, spectra and luminosity data • Emission states of black hole binares • Fast temporal variations: QPOs and broad power peaks • Energetics and key variables determining BHB radiation • Concluding remarks Hua Feng -- THCA jornal club

  3. Confirmed black hole binaries • Consequence of a stellar mass black hole • Compact object (emission peaked at X-ray band, fast variability) • Mass larger than a pressure supported object (3 Msun for a NS) • Mass function • 18 black hole binaries • 3 HMXBs (O/B star), X-ray persistent sources • Cyg X-1, LMC X-1, LMC X-3 • 15 LMXBs (1 Msun or less), X-ray transient sources, X-ray novae • A0620-00: 50 Crab (1975)  1 Crab (1995) • GRS 1915+105: remain bright since Aug 1992 • GX 339-4: frequent outbursts followed by very faint states Hua Feng -- THCA jornal club

  4. 18 confirmed BHBs Hua Feng -- THCA jornal club

  5. Black hole candidates • Radial velocity of the secondary cannot be measured • Characteristics of established BHBs • Ultrasoft X-ray spectrum (1-10 keV) • Power-law spectral tail extends beyond 20 keV • State transitions • Rapid temporal variability • None of these is proved to be entirely reliable (weakly magnetized NSs) • Absence of periodic pulsations or type I X-ray bursts Hua Feng -- THCA jornal club

  6. Hua Feng -- THCA jornal club

  7. Accretion onto black holestandard disk • Best-known model: standard thin disk model (Shukura & Sunyaev 1973) • Dimensionless angular momentum: a* = J/cMRg, a* = [0 1] • RISCO(a*=0) = 6Rg, RISCO(a*=1) = Rg • ISCO(a*=0) = 220 Hz (M/10Msun), ISCO(a*=1) = 1615 Hz (M/10Msun) • Kerr BH: rotational energy tapped electromagnetically (Blandford & Znajek 1977) • Energy loss: 0.057mc2 (Schwarzschild BH), 0.42mc2 (Kerr BH), 90% loss within 20Rg • Nonrelativistic approximation: Multicolor Disk (MCD), Ldisk = GMMdot/2Rin, T(R)  R-3/4 • A torque-free boundary condition at the ISCO  null dissipation • Relativistic corrections to the MCD model • e.g., Ebisawa et al. 1991; Zhang et al. 1997, Gierlinski et al. 2001 • MHD effects in the context of GR, radiation pressure and radiative transfer, BH rotation Hua Feng -- THCA jornal club

  8. Accretion onto black holeADAF • Advection-Dominated Accretion Flow (Narayan & Yi 1994, 1995; Narayan et al. 1996; Quataert & Narayan 1999) • Radiative efficiency ~0.1—1 % • In quiescent BHBs and some AGNs • With winds (ADIOs) and convection (CDAF) • State transitions: ADAF + MCD (Esin et al. 1997, 1998) • Limitations • Very high state • Simply ordering state with mdot • Not accounting for the dynamic behavior of the corona: flares, LFQPO • Radio emissions • “evaporation” process unclear • No quantitative model relating disk truncation radius to the accretion rate Hua Feng -- THCA jornal club

  9. Light curves of X-ray Novae x50 Hua Feng -- THCA jornal club

  10. Light curves of BHBs Hua Feng -- THCA jornal club

  11. Spectra of BHBs • Widely applicable models: diskbb (MCD) + power-law • A broad absorption feature above 7 keV • A reflection bump of X-ray by the disk • Spectral state transitions • Relativistic iron emission line • Super-Eddington luminosity • ULXs with 0.5-10 keV luminosities in 1039 – 1040.5 erg/s • Ledd = 1.25E38 M/Msun • Apparent differences between ULXs and BHBs in their spectra and duty cycles • 0.5-10 keV Lx/Ledd = 7.0, 3.5 and 1.4 for V4641 Sgr, 4U 1543-47 and GRS 1915+105, respectively Hua Feng -- THCA jornal club

  12. Emission states of BHBs • high/soft (HS) – thermal-dominated (TD) • low/hard (LH) – nonthermal dominated, radio jet associated • quiescent state • very high (VH), steep power-law state (SPL) • intermediate state • Luminosity is not a criterion for defining the states of BHBs Hua Feng -- THCA jornal club

  13. Quiescent state • An extraordinarily faint state Lx = 1030.5 – 1033.5 erg/s • Distinctly nonthermal and hard ( = 1.5 – 2.1) • Short-period system (A0620-00, P = 7.8 hrs), 1030 erg/s • Long-period system (V404 Cyg, P – 155.3 hr), 1033 erg/s • Mass transfer rates are driven by the nuclear evolution of their secondaries rather than by gravitational radiation (Menou et al. 1999) • Strong evidence of an event horizon • Relative faintness of BH navae than NS navae (in the context of ADAF) • Success of ADAF in BHB quiescence • Hard power-law spectra • Faintness of BHs relative to NSs • Several-day delay in the optical/UV light curve when X-ray novae go into outburst • Broadband spectrum: optical  X-ray • Disk truncation Hua Feng -- THCA jornal club

  14. Thermal-dominated (TD) state or high/soft (HS) state • Thermal component T 0.7-1.5 keV • Power-law component is steep ( = 2.1-4.8) and faint • Weak variability, 0.1-10 Hz rms 0.01-0.06 • QPO in 0.1-30 Hz are generally not seen; weak QPOs in two cases (27 Hz in GRO J1655-40 & 17 Hz in XTE J1550-564) • We thus define the TD state as the set of conditions for which • the disk–flux fraction is above 75% (2–20 keV), • the PDS shows no QPOs or very weak features (rms << 1%), and • the power continuum is also weak : r < 0.06 integrated over 0.1–10 Hz. • Ldisk  Tin4 with a constant Rin Hua Feng -- THCA jornal club

  15. Hard X-ray state associated with a steady radio jet • Presence of a compact and quasi-steady radio jet • VLBI images show resolved radio jet for GRS 1915+105 and Cyg X-1 • Correlated X-ray and radio intensities in the hard state for prolonged period • Quench of the persistent radio emission whenever an source exits the hard state and returns to the TD state • MCD >100 Rg and 0.024 keV  disk truncation. Broad Fe line and reflection  disk truncated or veiled? • Hard state characteristics • spectrum is dominated (> 80% at 2–20 keV) by a power–law spectrum, • spectral index is in the range 1.5 <  < 2.1 • integrated power continuum (0.1–10 Hz) is strong and typically in the range 0.1 < r < 0.3. Hua Feng -- THCA jornal club

  16. Steep power-law (SPL) state or very high (VH) state • Lx > 0.2LEdd,   2.4, power-law contribution 40-90% of total flux • Strength of the power-law component coincides generally with the onset X-ray QPOs in 0.1-30 Hz • Unbroken power-law spectra (100 keV cutoff for hard states) • The SPL state is defined • first by the presence of a power–law component in the X–ray spectrum with photon index  > 2.4. • secondly, either there are X–ray QPOs present (0.1–30 Hz) while the power–law contributes more than 20% of the total (unabsorbed) flux at 2–20 keV, or the power–law contributes more than 50% of the total flux without detections of QPOs. Hua Feng -- THCA jornal club

  17. Intermediate state • We conclude that it is inappropriate to refer to both the observations of XTE J1550–564 and the very different observations of GRO J1655–40 as representing a single BHB state, namely, the intermediate state. On the other hand, state transitions and hybrid emission properties are to be expected and X–ray spectra and PDS should be interpreted as intermediate states when necessary, while specifying which states can be combined to yield the observed X–ray properties. Hua Feng -- THCA jornal club

  18. Fast temporal variations: QPOs and broad power peak • QPO: / > 2 (FWHM), otherwise broad power peak • Low frequency QPO (LFQPO): 0.1-30 Hz • found in 14 BHBs • High frequency QPO (HFQPO): 40-450 Hz • Found in 4 BHBs Hua Feng -- THCA jornal club

  19. Low frequency QPOs and radiation mechanisms • LFQPOs are almost always seen during the SPL state • Exceedingly strong. Observed at E > 60 keV up to 120 keV in GRS 1915+105 • In several sources, the LFQPOs frequency is correlated with the total disk flux • LFQPOs provide a vital clue to the mechanism that couples the thermal and SPL compoents • LFQPOs can be quasi–stable features that persist for days or weeks • In a general sense, it can be argued that oscillations as distinct and strong as these QPOs (often with Q > 10), represent global requirements for an organized emitting region. • LFQPO frequencies are much lower than the Keplerian frequencies for orbits in the inner accretion disk • 3 Hz  100 Rg (10 Msun). Maximum X-ray emission lies in the range 1-10 Rg • oscillations are strongest at photon energies above 6 keV, i.e., where only the power–law component contributes substantially to the X–ray spectrum • disk oscillations (Titarchuk & Osherovich 2000) • radial oscillations of accretion structures such as shock fronts (Chakrabarti & Manickam 2000) • oscillations in a transition layer between the disk and a hotter Comptonizing region (Nobili et al. 2000). • accretion–ejection instability model invoking spiral waves in a magnetized disk (Tagger & Pellat 1999) with a transfer of energy out to the radius where material corotates with the spiral wave Hua Feng -- THCA jornal club

  20. HFQPOs and GR • Detected in 7 sources (4 BHBs and 3 BHCs) • three sources exhibit pairs of QPOs that have commensurate frequencies in a 3:2 ratio • GRO J1655-40 and XTE J1550-564: single pair • GRS 1915+105: two pairs • HFQPOs do not shift freely in frequency in response to luminosity changes Hua Feng -- THCA jornal club

  21. Fundamental frequency? Hua Feng -- THCA jornal club

  22. Division of spectral energy: disk and power-law components • The TD points (“x” symbol) for GRO J1655–40 and XTE J1550–564 (1998–99) appear well organized; they can be described as horizontal tracks in which accretion energy is freely converted to thermal radiation from the accretion disk • moderate Comptonization effects expected from MHD turbulence (e.g., Hawley & Krolik 2001) as these tracks curve upward at high luminosity • The hard states (circles) points form vertical tracks with only minor flux contributions from the disk • The SPL states (triangle) are widely diverse. Hua Feng -- THCA jornal club

  23. Key variables determining BHB radiation • Prior to RXTE era: states  luminosity  accretion rate and BH mass • BH spin and the angle between the spin and disk axes • MHD instability  nonthermal radiation • Magnetic fields  formation and collimation of jets • Ratio of magnetic to gas pressure  accretion physics • Global magnetic field geometry  formation of some X-ray state Hua Feng -- THCA jornal club

  24. Concluding remarks • The behavior of the massive compact objects reviewed herein supports the view that they are bona fide BHs, which are described by GR and were formed by the complete gravitational collapse of matter • GR effects • High frequency QPOs • Broad Iron line • Thermal radiation • Future measurements • LISA, MAXIM, Constellation-X, X-ray Timing Observatory (XTO, then times of effective area than RXTE with improved energy resolution) Hua Feng -- THCA jornal club

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