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.5.ppt

IV.5 Variability in X-ray Binary Systems

msec X-ray Pulsars Sources and Significance Timing and Spectral Properties

Aperiodic Variability in Accreting Neutron Stars Type I X-ray Bursts Type II X-ray Bursts Superbursts kHz QPOs

Aperiodic Variability in Black Holes Impulsive Relativistic Jets Weaker Types of Impulsive Jets Wild Instability Cycles in GRS1915+105

Msec X-ray PulsarsSource Spin (Hz) Orbit (hr) Bursts (Hz)

IGR J00291+5934 599 2.45

XTE J0929-314 185 0.73

XTE J1751-305 435 0.70

XTE J1807-294 191 0.58

SAX J1808.4-3658 401 2.00 bursts (401)

XTE J1814-338 314 4.27 bursts (314); not wd?

HETE J1900.1-2455 377 1.39 bursts

Swift J1756.9-2508 182 0.90

Characteristics:• Extremely compact binaries; wd companion (Rc~0.05 Ro; Mc~0.02 Mo)• Tip of reservoir of accretion-spun-up pulsars visible in X-rays• Key to spin-ID of burst oscillations • Key to inventory of spin distributions • Key toward a model for kHz QPOs

Msec X-ray Pulsars

XTE J0929-314: typical, faint transient peak ~ 30 mCrab (1.5-12 keV) outburst duration ~65 days

HETE J1900.1-2455: transient persists for 2+ years; brief turnoff ; early end of msec pulsations (Aug. 19, 2005)

Energy Spectra & Power Spectra of msec Pulsarsmsec X-ray pulsars resembleAtoll sources in hard state.

So why don’t atolls pulse(burst oscillations similar spin frequencies)

• B ranges different?• accretion plasma buries B?• HETEJ1900 may inform us!

Type I X-ray Bursts

Number of bursters ~80

Science Applications: Neutron-star finder Burst oscillations ( spin) Radius-expansion bursts

( distance estimate)

Redshifted abs. lines?(Cottam et al, 2003: 1? Case)

Test burst models Trace dM/dt at NS surface? Topic for BH event horizon

test (lack of bursts in BH)

Type I X-ray Bursts

Burst Oscillationse.g., Strohmayer

& Markwardt 1999

14 sources of BOs

max = spin

range: 45, 270-619 Hz

some frequency profiles are shorter or spotted (on/off)

amplitudes increase with energy (Muno et al. 2003)

Type I X-ray Bursts

Burst Oscillations

multiple max measures

From the same source give consistent results

Muno et al. 2002

Msec X-ray Pulsars and Burst Oscillations

Frequency (Hz)

Spin Distribution

Neutron Star Speed limit ~730 Hz(burst oscillations, radio pulsars, X-pulsars; Chakrabarty et al. 2003)

Why is limit < breakup freq.

• magnetic-accretion spin equilibrium? • Gravitational waves? (Wagoner 1984; Bildsten 1998)

Type I X-ray Bursts

Radius Expansion Burstse.g., Z-transient XTE J1701-462

Isolate burst spectrum(t)

Fit spectra to blackbody (R,t)

See R expansion

+ dip in T evolution

Eddinton Lx

distance estimate

(assume Mx, layer composition)

Look for consistent results

Rudimentary Elements of Bursts Models

Paradigm: thermonuclear explosion of H, He from accumulated, accreted matter on NS surface

Use Lx as a scale for dM/dt

Assume (vary) MNS and RNS

Assume (vary) composition Calculate (vary) T of subsurface layer (NS cooling model) Compute hydrostatic equilibrium Monitor (, T) for detonation conditions

Many complexities, e.g. differential rotation and turbulent mixing in surface layer (Prio & Bildsten 2007)

Bursts Models

Status of burst models(see Strohmayer & Bildsten 2006

many bursters on fast and slow side of burst rate expectations

Burst Oscillation Models

spot evolution

ray tracing for osc. amplitude(t))

Spitkovsky et al 2002, ApJ, 566, 1018

Type I bursts: huge science comeback; 1990s poster-child for “old and boring”

Type II X-ray Bursts

Number of sources 2 ; events are NOT thermal4U1730-33 (rapid burster + type I) ; GRO J1744-28 (bursting pulsar)

Linear E vs. t accretion instability

Cause unknown (magnetic?; high-rate ADAF?)

0 300 600Time (s)

Count rate

Rapid Burster; Inoue 2004, Adv. Sp. Res., 34, 2550

SuperBursts in Accreting Neutron Stars

Number of sources 8

duration: few to 10 hrtriggered by a type I burst

recurrence rate: year(s)

can excite transient pulsar at spin rate (1636-53)

model: C detonation in accretion/burst residue in subsurface layers

kHz QPOs

Number of sources 26 atolls 16

Z-type 8

msec pulsars 2

Properties• move in frequency (300-1200 Hz)• often twin, sometime solo• separation of twins varies slowly

kHz QPOs

QPO Scales

van der Klis 2006

Plot everything vs.upper kHz QPO

interpretationscontroversial

Upper kHz QPO

kHz QPOs

Current kHz QPO Models

Beat frequency model (Miller & Lamb)• twin peaks: Keplerian vs. NS surface footprint with RNS < RISCO

• twin peak separation interpreted as spin

• However, twin peak separation is spin or 0.5 spin

Disk Resonance (Abramowicz & Kluzniak)• TypIcial twin peaks are 600, 900 Hz 3:2 ratio• Resonance model for NS disks

Impulsive, Relativistic Jets in BH Binaries

GRS1915+105 jets

v > 0.9 c (Mirabel & Rodriguez 1994;

Fender et al. 1999)

Also GRO J1655-40, Cyg X-3,

XTE J1550-564 (see Fender 2006)

Special relativity demo; nut beware of assumption of bipolar symmetry

Ejection moment not observed

in X-rays

Black Holes in the Milky Way

Relativistic jets imaged in radioand also in X-rays (Chandra).

(Hannikainen et al. 2001; Corbel et al. 2002).

Baryonic content of MQ jets still uncertain,except for SS433

Impulsive, Relativistic Jets in BH Binaries

Small-scale impulsive jets• B-cycles of GRS1915+105 (Eikenberry et al. 1998; Fender + Pooley 1998)• strong evidence for disk:jet connection• other LC types (Eikenberry et al. 2007; Rodriguez et al. 2007)

More Complications: Fast X-ray Novae

SAX J1819.3-2525

(V4641 Sgr)

black hole binary

+ relativistic radio jets

‘Fast X-ray Nova’

20 min light curve,

Sept 15, 1999 (RXTE)

RXTE Observations of GRS1915+105

1996 – 2006: 1351 obs. (public data; 4.77 Ms)

785 data intervals (4.43 Ms)

Quasi-steady 428(rms < 16%; 1 s bins;

307 hard; 121 soft)

Variable Light Curves 357(rms > 16%)

Light Curve Types: Steady Variable

hard-steady 304 23 (-var )

soft-steady 64 0

soft-rolling 36 20

soft+dips 21 10

fast flare sequence + long min. 3 20

hard dip + trigger + soft spike 0 33

square waves 0 20

steady-flicker-dip sequence 0 5

flicker steady switching 0 16

flare-dip sequence + long min. 0 42

heartbeats (50 s) 0 89

dropouts to soft and variable 0 44

….new or inter- combinations 0 35 _______ _______

428 357

Steady Conditions: Color-Color Diagrams

Steady Conditions & Radio Flux

GRS1915+105: coded for radio flux (Ryle telescope, 15 GHz): (x x S < 5 mJy; 5 < S < 25; 25 < S < 75; S > 75 mJy ;

BHB Color-Intensity Diagrams

GRS1915+105/steady H1743-322 GX339-4

Fast QPOs in GRS1915+105

67 Hz: 28 (of 785) QPO detections ( > 4):

Sample: 67.37 Hz <Q> = 30.2

LC Type Detect (total) Frequency Q (freq./FWHM)

2 (64) 66.23 (0.34) 16

8 (56) 65.85 (0.24) 14

13 (31) 66.72 (0.21) 11

4 (16) 66.92 (0.70) 24

1 (20) 68.60 (0.93) 20

QPO Frequencies: 41, 67, 113, 165 Hz

67 Hz in “agitated soft state” or thermal:SPL intermediate

QPO near 67 Hz in type-averaged PDS[64][56][31]

QPOs in Variable States (avg. PDS; 2-40 kev)

[42] [89] [44]

GRS1915+105 Light Curves: Type

bright-hard zone contains a high-frequency QPO

GRS1915+105 : theta-blue

Power Density Spectra, blue regionQPO (9 ) at 165 +- 3 Hz; harmonic (330 Hz; 3.7 )

Q = 5, ampl = 2% (13-30 keV)

Colors resemble steep power-law state

GRS1915+105 Light Curves: Type

Long exposures, July 16-18, 2001. bright-hard zone: 113 Hz QPO at 6-40 keV

High Frequency QPOs from GRS1915+105

Type : bright-hard zone; 15-40 keV

Data Frequency Q (freq./FWHM)1997 Sept. 5-29 Remillard et al. 2002 165 (3) 5

1997 June - Oct. Belloni et al. 2006 166 (7) 2

All Type [44] (all HID zones) 165 (3) 4.7 (0.5)

Type : bright-hard zone; 6-40 keV

Data Frequency Q (freq./FWHM)2001 July 16-18 Remillard et al. 2004 113 (5) 2

All Type [42] (all HID zones) 112 (4) 2.2 (0.4)

GRS1915+105 Light Curves: Type

Profile variations within the group.

MIT undergraduate thesis: J. Z. Gazak

GRS1915+105 Light Curves: Type

Recurrence time and flare fractions for the group.

MIT undergraduate thesis: J. Z. Gazak

GRS1915+105 Light Curves: Type

Cycle zones for the group.

MIT undergraduate thesis: J. Z. Gazak

GRS1915+105 Light Curves: Type [82]

67 Hz in zone1

151 (4) Hz QPO

in zone 3

7 ; Q = 3.2

(8 +/- 3 % below 165 Hz)

keV: 2-40 6-40 15-40

QPOs in Variable States (avg. PDS; 2-40 kev)[42] [89] [44]

6-40 keV 6-40 keV 15-40 keV

MIRAX Support of Astrophysics

Properties Physical Models MIRAX Observations

Black Holes: mass Binary dynamics locate transients; optical teams

spin GR disk spectra thermal state measures & alerts

GR resonance (high-n QPOs) SPL state transitions and alerts

event horizon Type I burst models deep limits for burst function

jets Blandford-Znajek obs. moment of ejection; hard

GR MHD? Vertical B? state transitions; radio teams

accretion structures GR MHD (Prad regime) measure SPL high-Lx flares

MIRAX Support of Astrophysics

Properties Physical Models MIRAX Observations

Neutron Stars: mass Binary dynamics locate NS transients

radius kHz QPO models? bursts; atoll specra?

spin Binary evolution theory locate msxp transients

burst osc.; superburst osc.

magnetic field Mag. evol. models? pulsar cyclotron lines

SGR bursts; AXP bursts

internal structure NS structure models SGR oscillations

& crust Burst Models? Burst and superburst archive

jets MHD? hard state; transit.; radio team