XIV Advanced School on Astrophysics
Topic III: Observations of the Accretion Disks of
Black Holes and Neutron Stars
Ron Remillard
Kavli Institute for Astrophysics and Space Research
Massachusetts Institute of Technology http://xte.mit.edu/~rr/XIVschool_III.1.ppt

Topic III: General Outline
III.1 Accretion States of Black Hole Binaries (I)




X-ray Astronomy and Identification of Accreting Binaries
Properties of Compact Objects and Accretion Disks
Different X-ray States in Black Hole Binaries
Thermal State: Thermal Radiation from the Accretion Disk
III.2 Accretion States of Black Hole Binaries (II)




Observations of the Black Hole Hard State
Observations of the Steep Power Law State
Transients in Quiescence
X-ray Quasi-Periodic Oscillations in Black Hole Binaries
III.3 Accretion Disks around Neutron Stars



Timing Properties of Accreting Neutron Stars
Observations of Atoll Type Sources
New Interpretations for Z Type Sources

III.1 Accretion States of Black Hole Binaries (I)



Introduction to X-ray Binary Systems
Context for X-ray Astronomy
Classifications of X-ray Binaries



Black Holes, Neutron Stars, & Accretion Disks
Physical Properties
Measurement Techniques


X-ray States of Black Hole Binaries
Spectral/Timing Evolution of Accreting Black Holes
 Illustrations of Black Hole X-ray States


Thermal State: Hot Accretion Disk
Expectations and Definition of the Thermal State
 Building the Paradigm for the Thermal State

X-ray Photons

Wien’s Displacement Law (1893)
(wavelength ( l
) of max. energy flux in
I
( n
))
--- 10 Angstroms is very hot !
T = 5 x 10 7 o K / l max
(Angstroms)
Wilhelm Carl Werner Otto Fritz Franz Wien



X-rays: Photons 0.6-12 Angstroms  Energies 20-1 keV
Thermal Equivalent kT = 4 to 80 million o K
Heating mechanisms  non-thermal processes synchrotron radiation (high energy ein B field) inverse Compton (photon upscattered 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
Chandra (NASA Great Observatory)
XMM -Newton (European Space Agency)
Rossi X-ray Timing Explorer (NASA) MIRAX (small mission planned by Brazil)

Brightest X-ray Sources (10 to 10 -3 Crab)
Milky Way Sources primary X-spectrum
Accreting Neutron Stars
Atoll- and Z-sources
Accretion-powered Pulsars
Isolated Pulsars
Accreting Black Holes
Supernova Remnants thermal ; non-thermal hard state non-thermal mixed types thermal + non-thermal states thermal (shocks)
Stellar Coronae
Accreting White Dwarfs thermal ( B instability) thermal
Extragalactic
Active Galactic Nuclei
Blazars
Clusters of Galaxies
_____________ non-thermal (hard state) non-thermal (jets) thermal (bremsstrahlung)
1.0 Crab ~ 2.4x10
-8 erg cm -2 s -1 at 2-10 keV

Brightest X-ray Sources (10 to 10 -3 Crab)
Milky Way Sources primary X-spectrum accretion disk
Accreting Neutron Stars
Atoll- and Z-sources
Accretion-powered Pulsars
Isolated pulsars
Accreting Black Holes
Supernova Remnants thermal ; non-thermal hard state yes non-thermal mixed types thermal + non-thermal states yes thermal (shocks)
Stellar Coronae
Accreting White Dwarfs thermal ( B instability) thermal yes
Extragalactic
Active Galactic Nuclei
Blazars
Clusters of Galaxies
_____________ non-thermal (hard state) non-thermal (jets) thermal (bremsstrahlung)
1.0 Crab ~ 2.4x10
-8 erg cm -2 s -1 at 2-10 keV yes yes

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)

Properties of Black Holes



 mass: M x
Spin parameter: a
*
= cJ / GM x
2
( J = angular momentum ; dimensionless 0 < a
*
< 1 ; E rot
< 0.29 M ) charge: assume Q x
= 0 (local plasma prevents charge buildup) event horizon ! (math. surface of ‘no escape’)
(see Shapiro & Teukolsky 1983; Narayan 2004)
Can spin be measured?
Will quantitative, GR-based astrophysics be successful?
Accretion disk observations / accretion theory are the primary tools!

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 p
2 ( a x
+ a c
) 3 = G P 2 ( M x
+ M c
) center of mass: M x radial velocity amplitude K c a x
= M
= 2 p a c c a c sin i P -1
“Mass Function”: f(M) = P K 3 / 2 p
G = M x sin 3 ( i ) / (1 + M c
/ M x
) 2 < M x
Techniques to infer i and estimate M c
/M x
(see references)  M x

Compact Object Mass
Neutron Star Limit: 3 M o
(dP/d r
) 0.5
< c
Rhoades & Ruffini 1974
Chitre & Hartle 1976
Kalogera & Baym 1996
Black Holes (BH)
M x
= 4-20 M o
Neutron Stars (NS)
(X-ray & radio pulsars)
M x
~ 1.4 M o

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.

Identifications of X-ray Binaries
NS Binary: X-ray Bursts or Coherent X-ray Pulsations
NS Candidates: resemble NSBs in spectral & timing properties (limited info.)
BH Binary: Mass > 3 M o from binary analyses ; no NS properties
BH Candidate: BHB X-ray properties + no pulsations + no X-ray bursts
Milky Way
LMC nearby galaxies
--------------------total
Dynamical BHBs
18
BH Candidates
27
2 0
3 (e.g., M33-X7) (? many ULXs)
--------------------------------------------------------
23 27 + ?
Transients 17 25 + ?

Accretion Disks and the Inner Disk Boundary
Keplerian orbits for accreting 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
L(r) ~ d ( dE/dr ) = 0.5 e
G M x dt
= m r -2
L(r)
~
2 p r dr s
T 4  T(r)
~ r -3/4
Real physical model (and MHD simulations):
• transport & conserve angular momentum; outflow?, rad. efficiency ( e
)
• 3-D geometry (disk thickness, hydrostatic eq., radiative transfer)
• B -fields and instabilities
• GR effects (Innermost Stable Circular Orbit, grav. redshift, beaming)

Accretion onto Compact Objects
Compact Object M o
; <R km
> GMmR -1 / mc 2 Boundary Condition white dwarf 0.4-1.3 ; 6000 10 -4 crash on surface neutron star 1.4-2.0 ; ~10 0.2
crash on surface black hole 4-20 ; ~30 a
BH accretion disk
( a for 10M o
, a* = 0.5)
~60 a
~0.5 event horizon
~0.2
innermost stable circular orbit (ISCO)
Milky Way Today: 10 8 -10 9 BHs ; ~10 9 NSs ; > 10 10 WDs
(Timmes, Woosley & Weaver 1996; Adams and Laughlin 1996)

Inner Disk Boundary for Accretion Disks
 Black Holes: Innermost Stable Circular Orbit (ISCO)
BH spin a
*
: 0.0 0.5 0.75 0.9 0.98 1.0
-----------------------------------------------------
ISCO (R g
/ GM x
/c 2 ): 6.0 4.2 3.2 2.3 1.6 1.0
 Neutron Stars
Inner Accretion Disk (? R
NS
< R
ISCO
?)
NS Surface  Boundary Layer (2 nd heat source)
NS Spin (can influence bounday layer physics)
Magnetic Field Affects (Alfven Radius; control of inner accretion flow ; accretion focus at polar cap  pulsars)

Black Hole X-ray Transient (or ‘X-ray Nova’)
GRO J1655-40
First known outbursts: 1994-95;
(  ) 1996-97; 2005
Dynamical black hole binary
6.3 (
+
0.5) M o
Relativistic Jets in 1994
~Radio-quiet, 1996-97, 2005

Black Hole X-ray Transient
GRO J1655-40
 Different X-ray States

Illustrating 3 BH States of Active Accretion
Energy spectra Power density spectra
State physical picture
 steep power law Disk + ??
 thermal
 hard state
Energy (keV) Frequency (Hz)

Illustrating 3 BH States of Active Accretion
Energy spectra Power density spectra
State physical picture
 steep power law Disk + ??
 thermal
 hard state
Energy (keV) Frequency (Hz)

Time Series of Accretion States
GRO J1655-40
1996-97 outburst
Thermal x
Hard (jet) g
Steep Power Law
D
Intermediate O

Time Series of Accretion States
XTEJ1550-564
M x
= 9.6 + 1.2 M o
Thermal x
Hard (jet) g
Steep Power Law
D
Intermediate O

Thermal State of Black Hole Binaries
1.
Thermal State: radiant heat of the inner accretion disk disk fraction (2-20 keV) in energy spectrum: f disk power continuum (integrated 0.1-10 Hz):
> 75% ; rms < 0.075 ; no quasi-periodic oscillations (QPOs): a max
< 0.5%

Thermal State Paradigm
Theory: Hot gas in thin disk + viscous dissipation
Rel. MHD: Plasma + Magneto-Rotational Instability
 Thermal radiation ; weakly magnetized disk
Disk blackbody shape?
Disk blackbody energetics?
T(r) a r -p ; p ~ 0.7 (Kubota et al 2005)
(GR tweak of p=0.75)
Kubota & Done 2004;
Gierlinski & Done 2004

Other Measures of Disk Structure
Disk Structure Changes in Other States?
GX339-4 Relativistic Fe line e.g. Miller et al. 2004; but see Merloni & Fabian 2003

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

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

Thermal state  BH spin
Analyses of thermal state observations with new GR-disk models  quantitative measures of a
*
 Narayan Lecture (tomorrow)

Appendix: Tools for X-ray Data Analysis
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 Ka
(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

Appendix: Tools for X-ray Data Analysis
Method
Timing
Period Search
Application Comments
‘’
‘’
NS: X-ray Pulsars
NS or BH binary orbits
Long-term Periods
Quasi-Period Oscillations BH and NS low n
(0.1-50 Hz) high n
(50-1300 Hz) very slow (10 -6 to 10 -2 Hz) several types; measure dP/dt and pulse-profiles( E ) wind-caused for HMXB some LMXB eclipsers, dippers precessing disks ;
? slow waves in dM/dt ?
rich in detail common in some states
NS: var. n
; BH steady harmonics some BH: disk instability cycles

Appendix: Tools for X-ray Data Analysis
Method Application 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
Superbursts (many hours) two NS cases ; cause ??
C detonation in subsurface
? Probe NS interiors
‘’ Giant flares in Magnetars ? crust shifts + B reconnection
Progress?: coordinated timing / spectral analyses

References: Reviews
“Compact Stellar X-ray Sources”, eds. Lewin & van der Klis (2006) ;
16 chapters; some on ‘astro-ph’ preprint server: http://xxx.lanl.gov/form
Overview of Discovery
Rapid X-ray Variability
X-ray Bursts
Black Hole Binaries
Optical Observations
Isolated Neutron Stars
Jets
Accretion Theory
Magnetars
Psaltis van der Klis
Strohmayer & Bildsten
McClintock & Remillard
Charles & Coe
Kaspi, Roberts, & Harding
Fender
King
Wood & Thompson astro-ph/0410536 astro-ph/0410551 astro-ph/0301544 astro-ph/0306213 astro-ph/0308020 astro-ph/0402136 astro-ph/0303339 astro-ph/0301118 astro-ph/0406133
Other Reviews:
Narayan 2004, “Black Hole Event Horizon”, PThPS, 155, 263
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, 15, 1

References
Other references.: Most are in ARAA, 44, 49 or in
McClintock & Remillard 2006 (previous slide)
Additional References:
Adams and Laughlin 1996, ApJ, 468, 576
Done & Gierlinski 2003, MNRAS, 342, 1041
Gierlinski & Done 2004, MNRAS, 347, 885
Kubota & Done 2004, MNRAS, 353, 980
Timmes, Woosley, & Weaver 1996, ApJ, 457, 834
Power Density Spectra and deadtime corrections:
Leahy et al. 1983, ApJ, 266, 160
Zhang et al. 1995, ApJ, 449, 930
Dennis Wei undergrad thesis (MIT; 2006): http://xte.mit.edu/~rr/dwei_thesis.pdf