Ron Remillard Kavli Center for Astrophysics and Space Research

INPE Advanced Course on Compact Objects

Course IV: Accretion Processes in Neutron Stars & Black Holes

Ron RemillardKavli Center for Astrophysics and Space ResearchMassachusetts Institute of Technology

http://xte.mit.edu/~rr/inpe_IV.1.ppt

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 ()) --- 2 keV is hot !

T = 5 x 107 oK / 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 oK 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 Mo white dwarf degenerate isolated ; binaries; (0.4-1.3 Mo ; Earth-size) gas pressure cataclysmic

variables

8-25 Mo neutron star strong nuclear force radio pulsars ; hot-

(1.4-2.0 Mo ; R~10 km) isolated; X-ray pulsars; X-ray bursters

> 25 Mo black hole no classical forces accreting binaries

(3-16 Mo ; event horizon) quantum gravity? (X-ray sources)

Milky Way Today: 108-109 BHs ; ~109 NSs ; > 1010 WDs

(Timmes, Woosley & Weaver 1996; Adams and Laughlin 1996)

Collapsed Remnants of Old Stars

Compact Object <Mo> ; <Rcm> GMmR-1 / mc2 Boundary

white dwarf 0.6 ; 6x108 10-4 crash

neutron star 1.4 ; 106 0.2 crash

black hole 10 ; 3x106 0.5 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 ObjectsDynamical study: compact objectx and companion starc

(for binary period, P, and inclination angle, i )

Kepler’s 3rd Law: 4 2 (ax + ac)3 = GP2 (Mx + Mc)

center of mass: Mx ax = Mc ac

radial velocity amplitude Kc = 2 ac sin i P-1

“Mass Function”: f(M) = P K3 / 2G = Mx sin3(i) / (1 + Mc/Mx)2 < Mx

Dynamical Black Hole: Mx > 3 Mo (maximum for a neutron star)

BH Candidates: no pulsations + no X-ray bursts + properties of BHBs

Compact Object Mass

Neutron Star Limit: 3 Mo

(dP/d)0.5 < cRhoades & Ruffini 1974

Chitre & Hartle 1976

Kalogera & Baym 1996

Black Holes (BH)

Mx = 3-18 Mo

Neutron Stars (NS)

(X-ray & radio pulsars)

Mx ~ 1.4 Mo

Transients with Low-Mass Companions: Best Mx

Optical images of A0620-00; BH at 0.9 kpc

quiescence

outburst1975

P K3 / 2G = Mx sin3(i) / (1 + Mc/Mx)2

Optical Study of BH Binary in Quiescence

A0620-00

(X-ray Nova Mon 1975)

f(M) = 2.72 +/- 0.06 Mo

P = 0.323014(1) days

K4V companion

i ~ 60o

Mx = 7 +/- 3 Mo

Optical Study of BHB in Quiescence

Optical Photometry of

Gravity-distorted K4 star

Model( i, fstar , Mc/Mx , Tc, klimb, kgrav)

[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 18 25

LMC 2 0

local group 1 (M33) (? many ULXs)

--------------------- --------------------- ---------------------

total 21 25 + ?

Transients 17 23 + ?

Black Holes in the Milky Way

18 BHBs in Milky Way

16 fairly well constrained

(Jerry Orosz)

Scaled, tilted, andcolored for surface temp.

of companion star.

Inventory of Neutron-Star X-ray Sources

Subtype Typical Characteristics Number Transients

Atoll Sources Low-B; LMXBs; X-ray bursts; like BHBs ~100 ~60

Msec X-ray Pulsars 182-599 Hz ; atoll-like X-spectra 8 8

Z-sources high- Lx LMXBs; unique spectral/timing var. 9 1

HMXB or Pulsars hard spectrum + cutoff ; most are X-pulsars ~90 ~50

Magnetars Soft Gama Repeaters (4 + 1 cand.) 14 7

Anomalous X-ray Pul;sars (8 + 1 cand.)

Other Isolated Pulsars young SNRs; X-detect radio pulsars 70? 0?

---------- ---------

Total 291 126

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(1996-2007; 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 (Mx)

Spin NS: pulsations BH: infer a* = cJ / GMx2

BH event horizon compare NS accretion (hard surface) vs. BH (none?)

NS surface B field (<108 to >1015 G)

NS Interior (Eq. of state; burst models ; oscillation modes)

Understand Accretion Physicsorigin of different X-ray states ; accretion disk and Rin ; transient jets ;

hard X-rays (hot Comptonizing corona) ; quasi-periodic oscillations

primary variables: Mx , 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 Mx m r -1

Particle dE/dr = 0.5 G Mx m r -2

dL(r) ~ d (dE/dr) = 0.5 G Mx m r -2

dt

dL(r) 2r dr T4 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 pressureshear stress: tr = P (P = Pgas + Prad)

• thin disk: h << R• high radiative efficiency (local L release)

Makishima et al. 1986: apply to obs.T(r) r -3/4 ; L = 4 Rin

2 T4

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*: 0.0 0.5 0.75 0.9 0.98 1.0

-----------------------------------------------------

ISCO (Rg / GMx/c2): 6.0 4.2 3.2 2.3 1.6 1.0

Neutron Stars

Surface (and ? RNS < RISCO ?) Boundary Layer (2nd 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 1997Gierlinski et al. 2001; Li et al. 2005

Relativistic Accretion Disk: Spectral Models

GR Applications for Thermal State

e.g. kerrbb in xspecLi et al. 2005; Davis et al. 2005

• 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 Mx ; 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 Mx ; 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 (0.1-50 Hz) common in some states

high (50-1300 Hz) NS: var. ; BH steady harmonics

very slow (10-6 to 10-2 Hz) some BH: disk instability cycles

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 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 HorizonGame: model infall to hard surface (NS) vs. none (BH)

Topic Black Hole Neutron Star Model

Quiescent X-ray State

Measure Lx (erg s-1) 1031 few 1032 advection

Thermonuclear Bursts

Measure rate (at 0.1 LEdd) none 5x10-5 burst model

Thermal X-ray State

X-ray Spectrum max. fdisk > 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: http://xxx.lanl.gov/form

Overview of Discovery Psaltis astro-ph/0410536

Rapid X-ray Variability van der Klis astro-ph/0410551

X-ray Bursts Strohmayer & Bildsten astro-ph/0301544

Black Hole Binaries McClintock & Remillard astro-ph/0306213

Optical Observations Charles & Coe astro-ph/0308020

Fast Transients, Flashes Heise & in ‘t Zand ---

Isolated Neutron Stars Kaspi, Roberts, & Harding astro-ph/0402136

Jets Fender astro-ph/0303339

Accretion Theory King astro-ph/0301118

Magnetars Wood & Thompson astro-ph/0406133

References: ReviewsOther 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/07080148

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