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Ron Remillard Kavli Institute for Astrophysics and Space Research

XIV Advanced School on Astrophysics Topic III: Observations of the Accretion Disks of Black Holes and Neutron Stars III.3: Accretion Disks of Non-Magnetic Neutron Stars. Ron Remillard Kavli Institute for Astrophysics and Space Research Massachusetts Institute of Technology

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Ron Remillard Kavli Institute for Astrophysics and Space Research

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  1. 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

  2. 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. T4question 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

  3. Inventory of Neutron-Star X-ray Sources SubtypeTypical CharacteristicsNumberTransients 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 > 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

  4. X-ray Transients in the Milky Way • RXTE ASM: • 47 Persistent Sources> 20 mCrab (1.5 ASM c/s) • 83 Galactic Transients • (1996-2008; some recurrent) • Transients: timeline of science opportunities.

  5. Accreting NS Subclasses Cackett et al. (2006) • HMXB/pulsar (o) • Hard spectra: e.g., power-law photon index < 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

  6. 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:

  7. Accreting NS Subclasses • Atolls and Z-sources: LMXBs with binary periods< 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?

  8. Accreting NS Subclasses • Atolls and Z-sources: LMXBs with binary periods< 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?

  9. Energy Spectra & Power Spectra of Accreting NS

  10. Atoll-type Transients: Aql X-1, 4U1608-52 RXTE ASM: 10 outbursts per source

  11. 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

  12. 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

  13. 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) -------------- LBB (1038 erg/s at 10 kpc)

  14. Solution to problem with atoll soft state? Lin, Remillard, & Homan 2007 soft state: BB+MCD+weak BPL (constrained G < 2.5 ; Ebreak = 20) like double-thermal model of Mitsuda et al. 1984 hard state: Western (BB+BPL) ….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  Rns< RISCO? TMCDand TBB TMCDand TBB

  15. 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

  16. 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(BPL+MCD), 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.

  17. ASM Light Curves of bright Z Sources GX5-1 GX340+0 Cyg X-2 Sco X-1 GX349+2 GX17+2

  18. 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) GX349+2 GX17+2 HB NB FB

  19. Z Sources: Cyg X-2 group RXTE Observations 1996-2005 (each several ks) GX340+0 GX5-1 HB NB FB

  20. Z Source: Cyg X-2 Cyg X-2 RXTE observations “Z” moves around more than other sources

  21. Properties of Z-branches in GX 5-1 Flaring Branch (FB) Normal Branch (NB) Horizontal Branch (HB)

  22. Spectral Fits for Z Sources BeppoSAX Obs. of GX17+2 (Di Salvo et al. 2000) Horizontal Branch: 8% power law (1-200 keV). ; Normal branch: no hard tail upper HB lower NB

  23. Spectral Fits for Z Sources BeppoSAX Obs. of GX349+2 (Di Salvo et al. 2001; see also D’Amico et al. 2001) Normal Branch vertex has hard tail ; Flaring branch is usually very soft

  24. Transient Z-Source, XTE J1701-462 2006-2007 First and only Z-type transient RXTE: 866 obs. 3 Ms archive

  25. 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

  26. XTE J1701-462 Samples of Z’s 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

  27. XTE J1701-462 Spectral Fits Color-color spectral fit: Lx vs. T double-thermal model (disk+BB+CBPL) Cyg-Like Z Sco-like Z Atoll Stage  Reference lines: Radius from bursts Fit to constant RBB

  28. 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 TRa(M dM/dt R-3)1/4 • L aR2 TR4 • La(M dM/dt)2/3T4/3 Atoll stage: both disk & BB/boundary layer exhibit LaT4 (constant R)

  29. 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

  30. 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.

  31. Lower Z-vertex (NB:FB) NB:FB Vertex: local Eddington limit in the accretion disk? FB: disk tries to shrink toward ISCO from a point on this curve

  32. Evolution Speed along the FB NB:FB vertex appears more stable than the FB NB:FB Flaring BranchNB:FB Flaring Branch Vertex Vertex

  33. Upper Z-vertex (HB:NB) HB:NB Vertex: expansion of both disk and boundary layer with Lx what causes this turning point?

  34. 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)

  35. 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)

  36. 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

  37. 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 NB:FB 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 HB:NB vertex appears to be more stable than the NB, but its nature is somewhat mysterious.

  38. 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.

  39. References Reviews: Strohmayer & Bildsten 2006 (see reference list in Lecture 1) Van der Klis 2006 (see reference list in Lecture 1) Additional References: D’Amico et al. 2001, ApJ, 547, L147 DiSalvo et al. 2000, ApJ, 544, L119 DiSalvo et al. 2001, ApJ, 554, 49 Gilfanov et al. 2003, A&A, 410, 217 Hasinger et al. 1990, A&A, 235, 131 Homan et al. 2007, ApJ, 656, 420 Kuulkers et al. 1994, A&A, 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

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