inpe advanced course on compact objects course iv accretion processes in neutron stars black holes n.
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Ron Remillard Kavli Center for Astrophysics and Space Research

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  1. INPE Advanced Course on Compact ObjectsCourse IV: Accretion Processes in Neutron Stars & Black Holes Ron Remillard Kavli Center for Astrophysics and Space Research Massachusetts Institute of Technology

  2. IV.3 X-ray States of Accreting NSs • Classifying Atolls, Z-sources, and X-ray Pulsars • Spectral Shapes and X-ray Colors • Color-color and color-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 NSs • Hard State and Jets • Z Sources • Identifications and the two Groups • X-ray Power Density Spectra • X-ray Spectral Models • XTE J1701-462: the first Z-type transient

  3. 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

  4. Energy Spectra & Power Spectra of Accreting NS

  5. Accreting NS Subclasses • Atolls and Z-sources: X-ray spectra steeper than HMXB pulsars; • distinguished with color-color and color-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 curled) braches Top to bottom:

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

  7. 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), intermediate (island), hard (extreme island) states (Lin, Remillard, & Homan 2007)

  8. 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; Compt. dominates Lx Soft state: 3 keV corona; high opt. depth; thermal and Compt. share Lx

  9. Performance Test: L(BB or MCD) 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. 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)

  10. Solution to problem with atoll soft state? soft state: BB + MCD +weak BPL (constrainedG < 2.5 ; Ebreak = 20) hard state: Western (BB + BPL) top line: R = Rburst lower line: R = 0.2 Rburst LMCD (i=60o) and LBB (1038 erg/s at 10 kpc)  Rns< RISCO?

  11. Power Continuum vs. Comptonization 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

  12. Double-thermal Model: View of the Hard State LBB may track the accretion rate at NS surface If dm/dt (disk) = dm/dt (BL), then the hard state has too much rad. efficiency (e.g. line at 0.01 LEDD). Alternatively, along lines of constant L(BPL+MCD), the hard state shows 6X less dm/dt reaching the NS surface, compared to the soft state.

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

  14. Long-term color-color diagrams of Zs GX5-1 GX340+0 Cyg X-2

  15. Long-term color-color diagrams of Zs Sco X-1 GX349+2 gx17+2

  16. Properties of Z-branches Flaring Branch Normal Branch Horizontal Branch

  17. Hard X-ray Components of Z Sources RXTE Obs. of Sco X-1 (D’Amico et al. 2001) Transient hard tail ; not fixed in color-color branches ; but spectral shape does vary with color-color position

  18. 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

  19. Spectral Fits for Z Sources BeppoSAX Obs. of GX349+2 (Di Salvo et al. 2001) Normal Branch vertex has hard tail ; Flaring branch is very soft

  20. First Transient Z-Source: XTEJ1701-462 Homan et al. 2006 + Atels by Homan et al. in 2006 and 2007 t1: Zs like GX5-1 t2: Zs like Sco X-1 t3: X-ray bursts t4: Atoll behavior --t1 --t2 --t3 --t4 + efforts to model the X-ray spectra, for physical insights about Z-branches: HB, NB, FB