XIV%20Advanced%20School%20on%20Astrophysics%20Topic%20III:%20Observations%20of%20the%20Accretion%20Disks%20of%20Black%20Holes%20and%20Neutron%20Stars%20III.3:%20Accretion%20Disks%20of%20Non-Magnetic%20Neutron%20Stars

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XIV Advanced School on AstrophysicsTopic III
Observations of the Accretion Disks of Black
Holes and Neutron StarsIII.3 Accretion Disks
of Non-Magnetic Neutron Stars

• Ron Remillard
• Kavli Institute for Astrophysics and Space
  Research
• Massachusetts Institute of Technology
• http//xte.mit.edu/rr/XIVschool_III.3.ppt

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IV.3 X-ray States of Accreting NSs

• Classifying Atolls, Z-sources, and X-ray Pulsars
• Subclass Inventory and Spectral Shapes
• Color-Color and Hardness-Intensity Diagrams
• X-ray Spectra and Power-Density Spectra
• Soft and Hard States of Atoll Sources
• X-ray Spectra and the Model Ambiguity Problem
• The L vs. T4 question for Neutron Stars
• Interpreting the Boundary Layer and the Hard
  State
• Z Sources
• Z Source Properties and the Two Subroups
• XTE J1701-462 the first Z-type transient
• Phenomenological and Spectral Results for XTEJ
  1701
• Physical Models for Z-Branches and Vertices

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Inventory of Neutron-Star X-ray Sources

• Subtype Typical Characteristics Number
  Transients
• Accretors
• Atoll Sources LMXBs X-ray bursters 100
  60
• Msec X-ray Pulsars (182-599 Hz) atoll-like
  X-spectra 8 8
• Z-sources high- Lx LMXBs unique spectra/timing
  9 1
• HMXB or Pulsars hard spectrum P gt 3 d. many
  X-pulsars 90 50
• ---------------
• Non-accreting
• Magnetars Soft Gama Repeaters (4 1 cand.)
  14 7
• Anomalous X-ray Pulsars (8 1 cand.)
• Other Isolated Pulsars young SNRs X-detect
  radio pulsars 70? 0?
• ---------- ---------
  
• Totals 291 126

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X-ray Transients in the Milky Way

• RXTE ASM
• 47 Persistent Sources gt 20 mCrab (1.5 ASM c/s)
• 83 Galactic Transients
• (1996-2008 some recurrent)
• Transients timeline of science opportunities.

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Accreting NS Subclasses
Cackett et al. (2006)
HMXB/pulsar (o) Hard spectra e.g., power-law
photon index lt 1.0 at 1-20 keV ? easiest
distinguished via gross spectral shape weakly
magnetized, accreting NS (D) BH Binaries
and candidates (squares) filled symbol
persistent open symbol transient
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Accreting NS Subclasses
Atolls and Z-sources X-ray spectra are soft when
source is bright types distinguished with
color-color and hardness-intensity diagrams.
choose 4 energy bands A, B, C, D in order of
increasing energy soft color B/A hard
color D/C atoll transient
bright atoll source Z source
extreme island, island, banana branch
horizontal, normal, and and banana branches
(upper and lower) flaring (here dipping)
braches
Top to bottom
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Accreting NS Subclasses
Atolls and Z-sources LMXBs with binary periods
lt 2 d. diverse and complex
phenomenology (van der Klis 2006
Strohmayer Bildsten 2006) Spectra in different
states/branches disk boundary layer Power
rms/shape in each state/branch disk boundary
layer Type I X-ray bursts NS thermonuclear
burning Burst Oscillations (show NS spin) NS
thermonuclear burning Superbursts NS
thermonuclear burning Low-frequency QPOs (0.1
50 Hz) disk? kHz QPOs (200-1300 Hz) disk?
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Accreting NS Subclasses
Atolls and Z-sources LMXBs with binary periods
lt 2 d. diverse and complex
phenomenology (van der Klis 2006
Strohmayer Bildsten 2006) Spectra in different
states/branches disk boundary layer Power
rms/shape in each state/branch disk boundary
layer Type I X-ray bursts NS thermonuclear
burning Burst Oscillations (show NS spin) NS
thermonuclear burning Superbursts NS
thermonuclear burning Low-frequency QPOs (0.1
50 Hz) disk? kHz QPOs (200-1300 Hz) disk?
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Energy Spectra Power Spectra of Accreting NS
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Atoll-type Transients Aql X-1, 4U1608-52
RXTE ASM 10 outbursts per source
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Atoll-type Transients combine all outbursts
hard color 8.6-18 / 5.0-8.6 keV soft color
3.6-5.0 / 2.0-3.6 keV ? soft (banana),
transitional (island), hard (extreme island)
states
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Atoll Spectra Model Ambiguity (25 year debate)
Eastern Model A multi-color disk (MCD)
Comptonized blackbody (BB)
Western model BB Comptonized MCD For each,
Comptonization can be a simple slab model
(Tseed, Tcorona), or an uncoupled, broken
power law (BPL). All fits are good! Hard
state hot corona moderate opt. depth cool
BB or MCD Compton dominates Lx Soft state 3
keV corona high opt. depth thermal and
Compton share Lx
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Performance Test L (MCD. BB?) vs. T
Eastern Model MCD behavior unacceptable
in soft state Western model BB Lx
is not T4, in soft state, but physics of
boundary layer evolution is a complex
topic. ? Never see disk!! hard state Lx
growth is closer to T4 line (i.e., constant,
radius).
LMCD (1038 erg/s at 10 kpc) -------------- LB
B (1038 erg/s at 10 kpc)
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Solution to problem with atoll soft state?
Lin, Remillard, Homan 2007 soft state
BBMCDweak BPL (constrained G lt 2.5 Ebreak
20) like double-thermal model of Mitsuda et al.
1984 hard state Western (BBBPL) .like BH hard
state boundary layer!
LMCD and LBB (1038 erg/s at 10 kpc)
top line R Rburst lower line R 0.25 Rburst
? Rnslt RISCO?
TMCD and TBB TMCD and TBB
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Power rms vs. Comptonization fraction
2 Atoll transients
rms power in power density spectrum vs. fraction
of energy (2-20 keV) for Comptonization Black
Holes
Double-themal model atolls and BH very
similar In rms power vs. Comptonization fraction
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Double-thermal Model States vs. LBB
Does LBB track M-dot at the NS surface ?
If dm/dt (disk) dm/dt (BL), then hard state
has higher rad. efficiency than thermal
state. Alternatively, along L(BPLMCD), the hard
state shows 6X less dm/dt reaching the NS
surface, compared to the soft state. Neither
conclusion may hold if there are important
geometry issues, e.g. distributing some mass
outside the visible boundary layer area during
the hard state.
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ASM Light Curves of bright Z Sources
GX5-1 GX3400 Cyg X-2
Sco X-1 GX3492 GX172
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Z Sources Sco X-1 group

• Two groups of Z sources (Kuulkers et al. 1994)
• RXTE Obs. (several ks) 1996-2005 This group
  mainly occupies Normal Branch (NB) and Flaring
  Branches (FB)
• GX3492 GX172

HB
NB
FB
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Z Sources Cyg X-2 group

• RXTE Observations 1996-2005 (each several ks)
• GX3400 GX5-1

HB
NB
FB
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Z Source Cyg X-2

• Cyg X-2
• RXTE observations
• Z moves around
• more than other sources

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Properties of Z-branches in GX 5-1
Flaring Branch (FB) Normal Branch
(NB) Horizontal Branch (HB)
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Spectral Fits for Z Sources
BeppoSAX Obs. of GX172 (Di Salvo et al. 2000)
Horizontal Branch 8 power law (1-200 keV).
Normal branch no hard tail
upper HB lower NB
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Spectral Fits for Z Sources
BeppoSAX Obs. of GX3492 (Di Salvo et al. 2001
see also DAmico et al. 2001) Normal Branch
vertex has hard tail Flaring branch is usually
very soft
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Transient Z-Source, XTE J1701-462

• 2006-2007
• First and only
• Z-type transient
• RXTE 866 obs.
• 3 Ms archive

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Transient Z-Source, XTE J1701-462

? Cyg-like

• RXTE 866 obs.
• 3 Ms archive
• Horizontal (HB)
• Normal (NB)
• Flaring (FB)
• NB-FB Vertex

.... Sco-like Z source...
? atoll
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XTE J1701-462 Samples of Zs

Light curve color-color HID-steady
HID-variable

• 6 samples of the
• evolving Z pattern
• over the outburst
• Homan et al. 2007
• Lin, Remillard Homan 2008

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XTE J1701-462 Spectral Fits

Color-color spectral fit Lx vs.
T

• double-thermal
• model
• (diskBBCBPL)

Cyg-Like Z Sco-like Z Atoll Stage
? Reference lines Radius from bursts Fit to
constant RBB
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XTE J1701-462 Spectral Fits

not much change in disk ? NB BB increases R at
constant T
HB Cyg-like And Sco-like Zs Appear different?

• FB disk shrinks at constant dM/dt
• TR a (M dM/dt R-3)1/4
• L a R2 TR4
• L a (M dM/dt)2/3 T4/3

Atoll stage both disk BB/boundary
layer exhibit L a T4 (constant R)
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XTE J1701-462 Spectral Fits

Spectral Fit Results Lx vs. T
R vs. count rate

• double-thermal
• model
• (disk BB CBPL)
• Lin, Remillard, Homan 2008

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XTE J1701-462 Total Hardness-Intensity Diagram

• Upper and lower vertices form single lines on the
  HID.
• Lower vertex is a key to understanding global
  evolution and
• the physical processes for adjoining branches,
  i.e. the FB and NB.

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Lower Z-vertex (NBFB)

• NBFB Vertex local Eddington limit in the
  accretion disk?

FB disk tries to shrink toward ISCO from a point
on this curve
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Evolution Speed along the FB

NBFB vertex appears more stable than the FB

• NBFB Flaring Branch NBFB
  Flaring Branch
• Vertex Vertex

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Upper Z-vertex (HBNB)

• HBNB Vertex expansion of both disk and boundary
  layer with Lx
• what causes this turning point?

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Comptonization rms in power continuum

• Comparing Comptonizarion
• (fraction of flux in CBPL)
• with rms power fraction
• from PDS
• Increased continuum power
• in Cyg-like HB (only)
• tied to boundary layer,
• not power-law spectrum
• (confirming conclusion
• of Gilfanov et al. 2003)

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Comptonization in the HB

Samples Ia and IIIa All HB and upper vertex

• Does Compton energy
• along the HB
• come from the disk?
• Top panels L(disk)
• Bottom L(disk CBPL)

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Sco-like Z sources and dM/dt

• Hasinger van der Klis 1990 Increasing dM/dt
  along
• HB ? NB ? FB

HB
NB
FB

Lin, Remilard, Homan 2008 In a local Z, dM/dt
is almost constant with possible slight increase
along NB
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XTE J1701-462 summary

• Secular increases in dM/dt drive up the Z in the
  HID, while shifting the emphasis from the FB and
  lower vertex toward the upper vertex and the HB.
• Local Eddington limit is first seen in disk, and
  the NBFB vertex maps the disk response of RMCD
  to Lx (i.e., dM/dt), while RBB constant.
• Sco-like Z source phase
• At any point in the RMCD vs. Lx curve, the disk
  may try to shrink back towards the ISCO, which
  appears as movement along the FB
• Along the NB, the boundary layer brightens
  independently from the disk, perhaps in the onset
  of a radial accretion flow (small fraction of
  total)
• the HB shows the onset of Comptonization the
  HBNB vertex appears
• to be more stable than the NB, but its nature is
  somewhat mysterious.

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XTE J1701-462 summary

• Cyg-like Z source phase (higher dM/dt)
• the FB is the dipping type, and the spectral
  model does not fit the data well, thus preventing
  our interpretation
• along the NB, the boundary layer brightens,
  similar to the Sco-like phase but there are also
  changes in the disk, complicating interpretations
• HB-upturn shows increased Comptonization,
  resembling the Sco-like HB
• The non-upturn HB shows a large jump in rms
  without increased CBPL flux. The disk loses
  energy, while the boundary layer shows a slight
  gain and appears to be responsible for the rms
  power.
• Next investigations
• Use this spectral model to study kHz QPOs in all
  Z and atoll sources.

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References

• Reviews
• Strohmayer Bildsten 2006 (see reference list
  in Lecture 1)
• Van der Klis 2006 (see reference list in Lecture
  1)
• Additional References
• DAmico et al. 2001, ApJ, 547, L147
• DiSalvo et al. 2000, ApJ, 544, L119
• DiSalvo et al. 2001, ApJ, 554, 49
• Gilfanov et al. 2003, AA, 410, 217
• Hasinger et al. 1990, AA, 235, 131
• Homan et al. 2007, ApJ, 656, 420
• Kuulkers et al. 1994, AA, 289, 795
• Lin, Remillard, Homan 2007, ApJ, 667, 1073
• Lin, Remillard, Homan 2008, to be submitted
  Aug. 2008
• Mitsuda et al. 1984, PASJ, 36, 741