INPE Advanced Course on Compact Objects Course IV: Accretion Processes in Neutron Stars & Black Holes Ron Remillard Kavli Center for Astrophysics and Space Research Massachusetts Institute of Technology

Course IV Outline 1. Basic Elements of X-ray Binary Systems 2. Different States of Black-Hole Binaries 3. Weakly Magnetized Neutron-Star Binaries (Atolls and Z sources) 4. Periodic Variability: Orbits and Pulsars 5. Aperiodic Variability: Bursts, Flares & Instability Cycles

IV.1 Basic Elements of X-ray Binary Systems  Introduction X-ray Astronomy: window to hot and violent universe Endpoints of Stellar Evolution Science Goals for Observations of X-ray Binaries  Properties of Neutron Stars and Black Holes Physical Properties Mass Determinations Surveys of Different Types of Compact Objects  Fundamentals of Accretion Physics The Accretion Disk Relativistic Disk Models for Black Holes Non-thermal Radiation Processes Questions for General Relativity

X-ray Photons Wien’s Displacement Law (1893) (wavelength ( ) of max. energy flux in  ( )) keV is hot ! T = 5 x 10 7 o K / max (Angstroms) Wilhelm Carl Werner Otto Fritz Franz Wien X-rays: Photons Angstroms  Energies 20-1 keV  Thermal Equivalent kT = 4 to 80 million o K  Heating mechanisms  non-thermal processes synchrotron radiation (high energy e- in B field) inverse Compton (photon upscatter by high energy e-)

Window for Astrophysics from Space Photon transmission through the Galaxy X-rays: recover long-distance view at E > 1 keV

X-ray Telescopes in Space Mirrors (grazing incidence) + gratings? vs. Collimators (metal baffles) + Coded Masks (slit plate + shadows) Spectrometers: Semiconductors (Si); gas (Xe); CdZnTe pixels for hard-X Chandra (NASA Great Observatory) Rossi X-ray Timing Explorer (NASA)XMM-Newton (European Space Agency

Collapsed Remnants of Old Stars Initial Star Compact Object Support? Observed? < 8 M o white dwarf degenerate isolated ; binaries; ( M o ; Earth-size) gas pressure cataclysmic variables 8-25 M o neutron star strong nuclear force radio pulsars ; hot- ( M o ; R~10 km) isolated; X-ray pulsars; X-ray bursters > 25 M o black hole no classical forces accreting binaries (3-16 M o ; event horizon) quantum gravity? (X-ray sources) Milky Way Today: BHs ; ~10 9 NSs ; > WDs (Timmes, Woosley & Weaver 1996; Adams and Laughlin 1996)

Collapsed Remnants of Old Stars Compact Object ; GMmR -1 / mc 2 Boundary white dwarf 0.6 ; 6x crash neutron star 1.4 ; crash black hole 10 ; 3x event horizon

Binary Evolution for Accreting Compact Objects Scenario 1: Roche Lobe overflow More massive star dies first Binary separation can shrink (magnetic braking and/or grav. radiation) Companion may evolve and grow Common for Low-Mass (Companion) X-ray Binaries (LMXB) Scenario 2: Stellar Wind Accretion More massive star dies first Stellar wind captured (with possible inner accretion disk) Common for High-Mass (Companion) X-ray Binaries (HMXB)

Measuring Masses of Compact Objects Dynamical study: compact object x and companion star c (for binary period, P, and inclination angle, i ) Kepler’s 3 rd Law: 4  2 (a x + a c ) 3 = GP 2 (M x + M c ) center of mass:M x a x = M c a c radial velocity amplitude K c = 2  a c sin i P -1 “Mass Function”: f(M) = P K 3 / 2  G = M x sin 3 (i) / (1 + M c / M x ) 2 < M x Dynamical Black Hole: M x > 3 M o (maximum for a neutron star) BH Candidates: no pulsations + no X-ray bursts + properties of BHBs

Compact Object Mass Neutron Star Limit: 3 M o (dP/d  ) 0.5 < c Rhoades & Ruffini 1974 Chitre & Hartle 1976 Kalogera & Baym 1996 Black Holes (BH) M x = 3-18 M o Neutron Stars (NS) (X-ray & radio pulsars) M x ~ 1.4 M o

Transients with Low-Mass Companions: Best M x Optical images of A ; BH at 0.9 kpc quiescence outburst 1975 P K 3 / 2  G = M x sin 3 (i) / (1 + M c /M x ) 2

Optical Study of BH Binary in Quiescence A (X-ray Nova Mon 1975) f(M) = / M o P = (1) days K4V companion i ~ 60 o M x = 7 +/- 3 M o

Optical Study of BHB in Quiescence Optical Photometry of Gravity-distorted K4 star Model( i, f star, M c /M x, T c, k limb, k grav ) [residual disk; star spots] Other techniques:  Rotational broadening of absorption lines  Doppler curve of emission lines (residual disk) …… worse problems

Inventory of Black Hole Binaries BH Binary: Mass from binary analyses BH Candidate: BHB X-ray properties + no pulsations + no X-ray bursts Dynamical BHBs BH Candidates Milky Way LMC 2 0 local group 1 (M33) (? many ULXs) total ? Transients ?

Black Holes in the Milky Way 18 BHBs in Milky Way 16 fairly well constrained  (Jerry Orosz) Scaled, tilted, and colored for surface temp. of companion star.

Inventory of Neutron-Star X-ray Sources SubtypeTypical Characteristics Number Transients Atoll Sources Low-B; LMXBs; X-ray bursts; like BHBs ~100 ~60 Msec X-ray Pulsars Hz ; atoll-like X-spectra 88 Z-sources high- L x LMXBs; unique spectral/timing var. 91 HMXB or Pulsarshard spectrum + cutoff ; most are X-pulsars ~90 ~50 MagnetarsSoft Gama Repeaters (4 + 1 cand.) 147 Anomalous X-ray Pul;sars (8 + 1 cand.) Other Isolated Pulsars young SNRs; X-detect radio pulsars 70? 0? Total Cataloged radio pulsars number approaching 2000?

X-ray Transients in the Milky Way RXTE ASM: 47 Persistent Sources > 20 mCrab (1.5 ASM c/s) 80 Galactic Transients ( ; some recurrent) Transients: timeline of science opportunities.

Science Goals for Observing X-ray Binaries Locate stellar black holes and neutron stars 100% of BHs from X-ray sources ; special applications for X-selected NSs Measure Physical Properties of Compact Objects Mass (M x ) Spin NS: pulsations BH: infer a * = cJ / GM x 2 BH event horizon compare NS accretion (hard surface) vs. BH (none?) NS surface B field ( G) NS Interior (Eq. of state; burst models ; oscillation modes) Understand Accretion Physics origin of different X-ray states ; accretion disk and R in ; transient jets ; hard X-rays (hot Comptonizing corona) ; quasi-periodic oscillations primary variables: M x, dM/dt, spin ; other variables: i,  spin, surface B (NS), global B, plasma  ?

Accretion Disks and the Inner Disk Boundary Keplerian Orbits for sample m E(r)= U+K = 0.5 U(r) = -0.5 G M x m r -1 Particle dE/dr = 0.5 G M x m r -2  dL(r) ~ d (dE/dr) = 0.5  G M x m r -2 dt dL(r)  2  r dr  T 4  T(r)  r -3/4 Real physical model: conserve angular momentum (viscosity); outflow?, rad. efficiency (  ) 3-D geometry (disk thickness, hydrostatic eq., radiative transfer) B-fields and instabilities GR effects (Innermost Stable Circular Orbit, grav. redshift, beaming)

Toward a Complete Model of Accretion Disks 1.Shakura & Sunyaev  -disk (1973) viscosity scales with total pressure shear stress: t r  =  P (P = P gas + P rad ) thin disk: h << R high radiative efficiency (local L release) Makishima et al. 1986: apply to obs. T(r)  r -3/4 ; L = 4  R in 2  T 4 2. MRI: Magneto-Rotational Instability (Balbus &Hawley 1991) MHD simulations: plasma eddies with local B, are sheared in a rotating disk; this process transports angular momentum outward. Continued MHD accretion simulations in General Relativity (e.g. Hawley & Balbus 2002; DeVilliers, Hawley, & Krolik 2003; McKinney & Gammie 2004) no dissipation (radiation) included in GR MHD simulations, thus far problem : no independent measure of mass accretion rate

Black Holes: Innermost Stable Circular Orbit (ISCO) BH spin a * : ISCO (R g / GM x /c 2 ): Neutron Stars Surface (and ? R NS < R ISCO ?)  Boundary Layer (2 nd heat source) Magnetic Field Affects (Alfven Radius; control of inner accretion flow ; accretion focus at polar cap  pulsars) Inner Disk Boundary for Accretion Disks

Emissivity vs. Radius in the Accretion Disk GR Applications for Thermal State Shakura & Sunyaev 1973; Makishima et al. 1986;Page & Thorne 1974; Zhang, Cui, & Chen 1997 Gierlinski et al. 2001; Li et al. 2005

Relativistic Accretion Disk: Spectral Models GR Applications for Thermal State e.g. kerrbb in xspec Li et al. 2005; Davis et al Integrate over disk and B (T) Correct for GR effects (grav-z, Doppler, grav-focusing) Correct for radiative transfer

Method Application Comments Images impulsive BJB jets two cases (Chandra) Spectrum Model Continuum accretion disk BH: infer a * if known M x ; d Model Hard X-rays hot corona / Comptonization two types: (1) jet ; (2) ??? Spectral Lines BH: broad Fe K-  (6.4 keV) corona fluoresces inner disk emission profile  M x ; a * ‘’ high-ioniz. absorption lines seen in a few BHs variable, magnetized disk? ‘’ redshifted absorption line 1 NS?: surface grav. redshift Tools for X-ray Data Analysis

Method Application Comments Timing Period Search NS: X-ray Pulsars several types; measure dP/dt and pulse-profiles(E) ‘’ NS or BH binary orbits wind-caused for HMXB some LMXB eclipsers, dippers ‘’ Long-term Periods precessing disks ; ? slow waves in dM/dt ? Quasi-Period Oscillations BH and NS rich in detail low ( Hz) common in some states high ( Hz) NS: var. ; BH steady harmonics very slow (10 -6 to Hz) some BH: disk instability cycles Tools for X-ray Data Analysis

MethodApplication Comments Timing Aperiodic Phenoma ‘’Type I X-ray Bursts in NS thermonucl. explosions on surface ID as NS ; oscillations  spin ; infer distance ; physical models improving ‘’Type II X-ray Bursts two NS cases ; cause ?? ‘’Superbursts (many hours) C detonation in subsurface ? Probe NS interiors ‘’Giant flares in Magnetars ? crust shifts + B reconnection Progress?: coordinated timing / spectral analyses Tools for X-ray Data Analysis

Defining X-ray States in BHB? Thermal State: inner accretion disk X-ray states  Lecture IV.2

Searches for the Event Horizon Game: model infall to hard surface (NS) vs. none (BH) Topic Black Hole Neutron StarModel Quiescent X-ray State Measure L x (erg s -1 ) few advection Thermonuclear Bursts Measure rate (at 0.1 L Edd )none 5x10 -5 burst model Thermal X-ray State X-ray Spectrum max. f disk > 90% 80%boundary layer (Narayan 2004 ; Narayan & Heyl 2002; Remillard et al. 2006; Done & Gierlinski 2003)

References: Reviews “Compact Stellar X-ray Sources”, eds. Lewin & van der Klis (2006) ; 16 chapters; some on ‘astro-ph’ preprint server: Overview of DiscoveryPsaltis astro-ph/ Rapid X-ray Variability van der Klis astro-ph/ X-ray BurstsStrohmayer & Bildsten astro-ph/ Black Hole BinariesMcClintock & Remillard astro-ph/ Optical ObservationsCharles & Coe astro-ph/ Fast Transients, FlashesHeise & in ‘t Zand --- Isolated Neutron StarsKaspi, Roberts, & Harding astro-ph/ JetsFender astro-ph/ Accretion TheoryKing astro-ph/ MagnetarsWood & Thompson astro-ph/

References: Reviews Other Reviews: Remillard & McClintock 2006, "X-Ray Properties of Black-Hole Binaries", ARAA, 44, 49 Done. Gierlinski, & Kubota 2007, “Modelling the behaviour of accretion flows in X-ray binaries”, A&A Reviews, in press, astro-ph/ X-ray Binary Catalogs: (HMXB) Liu, van Paradijs, & van den Heuvel 2006, A&A, 455, 1165 (LMXB) Liu, van Paradijs, & van den Heuvel 2007, A&A, 469, 807