1. 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 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. T 4 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

3. Inventory of Neutron-Star X-ray Sources SubtypeTypical Characteristics Number Transients Accretors: Atoll Sources LMXBs; X-ray bursters ~100 ~60 Msec X-ray Pulsars (182-599 Hz) ; atoll-like X-spectra 88 Z-sourceshigh- L x LMXBs; unique spectra/timing 91 HMXB or Pulsarshard spectrum; P > 3 d.; many X-pulsars ~90 ~50 --------------- Non-accreting: MagnetarsSoft Gama Repeaters (4 + 1 cand.) 147 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 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 (  ) BH Binaries and candidates (squares) filled symbol: persistent open symbol: transient Cackett et al. (2006)

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/Ahard 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/branchesdisk & boundary layer Power rms/shape in each state/branchdisk & boundary layer Type I X-ray burstsNS & thermonuclear burning Burst Oscillations (show NS spin)NS & thermonuclear burning SuperburstsNS & 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/branchesdisk & boundary layer Power rms/shape in each state/branchdisk & boundary layer Type I X-ray burstsNS & thermonuclear burning Burst Oscillations (show NS spin)NS & thermonuclear burning SuperburstsNS & 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 (T seed, T corona ), or an uncoupled, broken power law (BPL). All fits are good! Hard state: hot corona; moderate opt. depth; cool BB or MCD; Compton dominates L x Soft state: 3 keV corona; high opt. depth; thermal and Compton share L x

13. Performance Test: L (MCD. BB?) vs. T Eastern Model: MCD behavior unacceptable in soft state Western model: BB L x is not T 4, in soft state, but physics of boundary layer evolution is a complex topic.  Never see disk!! hard state: L x growth is closer to T 4 line (i.e., constant, radius). L MCD (10 38 erg/s at 10 kpc) -------------- L BB (10 38 erg/s at 10 kpc)

14. Solution to problem with atoll soft state? Lin, Remillard, & Homan 2007 soft state: BB+MCD+weak BPL (constrained  < 2.5 ; E break = 20) like double-thermal model of Mitsuda et al. 1984 hard state: Western (BB+BPL) ….like BH hard state + boundary layer! L MCD and L BB (10 38 erg/s at 10 kpc) top line: R = R burst lower line: R = 0.25 R burst  R ns < R ISCO ? T MCD and T BB

15. Power rms vs. Comptonization fraction Double-themal model: atolls and BH very similar In rms power vs. Comptonization fraction rms power in power density spectrum vs. fraction of energy (2-20 keV) for Comptonization Black Holes: 2 Atoll transients

16. Double-thermal Model: States vs. L BB 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. Does L BB track M-dot at the NS surface ?

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

18. 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 Z Sources: Sco X-1 group FB NB HB

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

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

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

25. RXTE: 866 obs. 3 Ms archive Horizontal (HB) Normal (NB) Flaring (FB) NB-FB Vertex Transient Z-Source, XTE J1701-462  Cyg-like ………….... Sco-like Z source…..…….  atoll

26. 6 samples of the evolving Z pattern over the outburst Homan et al. 2007 Lin, Remillard & Homan 2008 XTE J1701-462 Samples of Z’s Light curve color-color HID-steady HID-variable

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

28. XTE J1701-462 Spectral Fits  FB: disk shrinks at constant dM/dt T R  (M dM/dt R -3 ) 1/4 L  R 2 T R 4 L  (M dM/dt) 2/3 T 4/3 not much change in disk  NB: BB increases R at constant T HB: Cyg-like And Sco-like Zs Appear different? Atoll stage: both disk & BB/boundary layer exhibit L  T 4 (constant R)

29. double-thermal model (disk + BB + CBPL) Lin, Remillard, & Homan 2008 XTE J1701-462 Spectral Fits Spectral Fit Results L x vs. T R vs. count rate

30. 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. XTE J1701-462: Total Hardness-Intensity Diagram

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

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

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

34. 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) Comptonization & rms in power continuum

35. Does Compton energy along the HB come from the disk? Top panels: L(disk) Bottom: L(disk + CBPL) Comptonization in the HB Samples Ia and IIIa All HB and upper vertex

36. Hasinger & van der Klis 1990: Increasing dM/dt along HB  NB  FB Sco-like Z sources and dM/dt HB NB FB Lin, Remilard, & Homan 2008: In a local Z, dM/dt is almost constant with possible slight increase along NB

37. 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 R MCD to L x (i.e., dM/dt), while R BB ~ constant. Sco-like Z source phase: At any point in the R MCD vs. L x 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. XTE J1701-462: summary

38. 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. XTE J1701-462: summary

39. 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 References