INPE Advanced Course on Compact Objects

Course IV: Accretion Processes in Neutron Stars & Black HolesRon RemillardKavli Center for Astrophysics and Space ResearchMassachusetts Institute of Technology

http://xte.mit.edu/~rr/INPE_IV.3.ppt

IV.3 X-ray States of Accreting NSsClassifying Atolls, Z-sources, and X-ray PulsarsSpectral Shapes and X-ray ColorsColor-color and color-intensity diagramsX-ray spectra and power-density spectra

Soft and Hard States of Atoll SourcesX-ray Spectra and the Model Ambiguity ProblemThe L vs. T4 question for NSsHard State and Jets

Z SourcesIdentifications and the two GroupsX-ray Power Density SpectraX-ray Spectral ModelsXTE J1701-462: the first Z-type transient

Accreting NS SubclassesHMXB/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 andcandidates (squares)

filled symbol: persistentopen symbol: transientCackett et al. (2006)

Energy Spectra & Power Spectra of Accreting NS

Accreting NS SubclassesAtolls 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/Ahard color = D/C

atoll transient bright atoll source Z sourceextreme island, island, banana branch horizontal, normal, andand banana branches (upper and lower) flaring (here curled) brachesTop to bottom:

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

Atoll-type Transients: combine all outburstshard 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)

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

Performance Test: L (BB or MCD) vs. TEastern 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/sat 10 kpc)

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LBB(1038 erg/sat 10 kpc)

Solution to problem with atoll soft state?soft state: BB + MCD + weak BPL (constrained G < 2.5 ; Ebreak = 20)

hard state: Western (BB + BPL)LMCD (i=60o)andLBB

(1038 erg/sat 10 kpc)

top line:R = Rburst

lower line:R = 0.2 Rburst Rns< RISCO?

Power Continuum vs. ComptonizationDouble-themal model: atolls and BH very similarIn rms power vs. Comptonization fractionrms power in power density spectrumvs.fraction of energy (2-20 keV) for Comptonization

Black Holes: 2 Atoll transients

Double-thermal Model: View of the Hard StateLBB 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.

ASM Light Curves of Z SourcesGX5-1

GX340+0

Cyg X-2Sco X-1

GX349+2

GX17+2

Long-term color-color diagrams of ZsGX5-1 GX340+0 Cyg X-2

Long-term color-color diagrams of ZsSco X-1 GX349+2 gx17+2

Properties of Z-branchesFlaring Branch

Normal Branch

Horizontal Branch

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

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

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

First Transient Z-Source: XTEJ1701-462--t1--t2--t3--t4Homan 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+ efforts to model the X-ray spectra, for physical insights about Z-branches: HB, NB, FB

Ok